Added a way to read what the AI received from your sources (#1100)

Co-authored-by: Thorsten Sommer <SommerEngineering@users.noreply.github.com>

app/MindWork AI Studio/Tools/Services/ArbitraryFileDataSegment.cs

@@ -5,5 +5,5 @@ namespace AIStudio.Tools.Services;
 /// </summary>
 /// <param name="Content">The extracted text.</param>
 /// <param name="TokenCount">The number of tokens of that text.</param>
-/// <param name="PageNumber">The page that text came from, or null when it has none. Presentations and spreadsheets have none.</param>
-public sealed record ArbitraryFileDataSegment(string Content, int TokenCount, int? PageNumber);
+/// <param name="Location">Where that text came from: its page, its sheet and row, or its line. Presentations have none.</param>
+public sealed record ArbitraryFileDataSegment(string Content, int TokenCount, SourceLocation Location);

app/MindWork AI Studio/Tools/Services/ConversationTokenCounter.cs

@@ -5,6 +5,7 @@ using System.Text;
 using AIStudio.Chat;
 using AIStudio.Provider;
 using AIStudio.Settings;
+using AIStudio.Tools.Databases;
 
 namespace AIStudio.Tools.Services;
 
@@ -28,7 +29,7 @@ using Provider = AIStudio.Settings.Provider;
 /// provider, the built-in one does the counting, and two tokenizers disagree by a few percent on
 /// prose and by more than that on code.
 /// </remarks>
-public sealed class ConversationTokenCounter(RustService rustService, ILogger<ConversationTokenCounter> logger)
+public sealed class ConversationTokenCounter(RustService rustService, DatabaseClientProvider databaseClientProvider, ILogger<ConversationTokenCounter> logger)
 {
     /// <summary>
     /// How much text goes into one counting request.
@@ -267,6 +268,29 @@ public sealed class ConversationTokenCounter(RustService rustService, ILogger<Co
     /// </remarks>
     private async Task<int> CountDocumentAsync(Provider provider, FileAttachment document, CancellationToken token)
     {
+        //
+        // A document sent before goes out as the text it was stored with, see FileAttachment.ProvenanceId,
+        // so that is what counts, whatever its file says by now. The entry never changes, so its id is
+        // key enough:
+        //
+        if (document.ProvenanceId is { } provenanceId)
+        {
+            var storedKey = $"{provider.TokenizerPath}{KEY_SEPARATOR}{provenanceId}";
+            if (this.counted.TryGetValue(storedKey, out var storedTokens))
+                return storedTokens;
+
+            var store = await databaseClientProvider.GetProvenanceStoreAsync(token);
+            var entries = await store.GetEntriesAsync([provenanceId], token);
+            if (entries.TryGetValue(provenanceId, out var entry))
+            {
+                storedTokens = await this.CountTextAsync(provider, entry.Content, token);
+                this.counted[storedKey] = storedTokens;
+                return storedTokens;
+            }
+
+            // Without its entry, the request reads the file instead, and so does the count.
+        }
+
         var file = new FileInfo(document.FilePath);
         if (!file.Exists)
             return 0;

app/MindWork AI Studio/Tools/Services/DataBackupService.cs

@@ -5,6 +5,7 @@ using AIStudio.Settings;
 using AIStudio.Tools.AIJobs;
 using AIStudio.Tools.Databases;
 using AIStudio.Tools.Databases.IndexStore;
+using AIStudio.Tools.Databases.ProvenanceStore;
 using AIStudio.Tools.Databases.VectorStore;
 using AIStudio.Tools.DataBackup;
 using AIStudio.Tools.Media;
@@ -153,7 +154,7 @@ public sealed class DataBackupService(ILogger<DataBackupService> logger, Setting
     }
 
     /// <summary>
-    /// Copies the settings and the indexes, and writes them into the backup together with the rest of the data.
+    /// Copies the settings, the provenance store and the indexes, and writes them into the backup together with the rest of the data.
     /// </summary>
     /// <param name="archivePath">The file of the backup.</param>
     /// <param name="progress">Receives how far writing got.</param>
@@ -162,6 +163,7 @@ public sealed class DataBackupService(ILogger<DataBackupService> logger, Setting
     private async Task<DataBackupManifest> WriteBackupAsync(string archivePath, IProgress<DataBackupProgress> progress, CancellationToken token)
     {
         var indexCopiesDirectory = string.Empty;
+        var provenanceCopyDirectory = string.Empty;
         try
         {
             var dataDirectory = SettingsManager.DataDirectory ?? throw new InvalidOperationException("The data directory is not known yet.");
@@ -170,9 +172,14 @@ public sealed class DataBackupService(ILogger<DataBackupService> logger, Setting
             var settingsJson = JsonSerializer.Serialize(settings, SettingsManager.JSON_OPTIONS);
             var organizationPluginFolders = DataBackupContents.FindOrganizationPluginsAmongUserPlugins(PluginFactory.AvailablePlugins.OfType<IAvailablePlugin>(), dataDirectory);
 
+            //
+            // The texts the chats received are copied once the chats themselves are written, cf.
+            // DataBackupSources.CopyProvenanceStoreAsync: an answer completed meanwhile then still
+            // finds its texts in the backup.
+            //
             indexCopiesDirectory = await this.CopyIndexesAsync(dataDirectory, token);
 
-            var sources = new DataBackupSources(dataDirectory, configDirectory, settingsJson, indexCopiesDirectory, organizationPluginFolders);
+            var sources = new DataBackupSources(dataDirectory, configDirectory, settingsJson, indexCopiesDirectory, organizationPluginFolders, async copyToken => provenanceCopyDirectory = await this.CopyProvenanceStoreAsync(dataDirectory, copyToken));
             var manifest = new DataBackupManifest(
                 DataBackupFormat.FORMAT_VERSION,
                 Assembly.GetExecutingAssembly().GetCustomAttribute<MetaDataAttribute>()?.Version ?? "unknown",
@@ -188,7 +195,8 @@ public sealed class DataBackupService(ILogger<DataBackupService> logger, Setting
         }
         finally
         {
-            this.TryDeleteIndexCopies(indexCopiesDirectory);
+            this.TryDeleteCopies(indexCopiesDirectory);
+            this.TryDeleteCopies(provenanceCopyDirectory);
         }
     }
 
@@ -253,11 +261,56 @@ public sealed class DataBackupService(ILogger<DataBackupService> logger, Setting
         }
         catch
         {
-            this.TryDeleteIndexCopies(preparation.StagingPath);
+            this.TryDeleteCopies(preparation.StagingPath);
             throw;
         }
     }
 
+    /// <summary>
+    /// Copies the provenance store, for every backup.
+    /// </summary>
+    /// <remarks>
+    /// The store belongs to the chats, which every backup holds: without it, the chats of a backup
+    /// would refer to contents it lacks. So it is copied independently of the indexes, also when the
+    /// backup leaves those out.<br/><br/>
+    ///
+    /// A store which AI Studio could not open is taken from the data folder as it lies there:
+    /// nothing writes to it then, and the backup keeps whatever there is. So is a store which could
+    /// not be copied, e.g., since it is damaged: that must not cost the backup of the chats.
+    /// </remarks>
+    /// <param name="dataDirectory">The data folder, which holds the directory of the copies.</param>
+    /// <param name="token">The cancellation token.</param>
+    /// <returns>The directory of the copy, in the layout of the data folder, or an empty string when the backup takes the store from the data folder.</returns>
+    private async Task<string> CopyProvenanceStoreAsync(string dataDirectory, CancellationToken token)
+    {
+        var provenanceStore = await databaseClientProvider.GetProvenanceStoreAsync(token);
+        if (provenanceStore is NoProvenanceStoreClient)
+        {
+            logger.LogWarning("The provenance store is not available, so the backup takes it from the data folder as it lies there.");
+            return string.Empty;
+        }
+
+        // In the same directory as the copies of the vector stores, which the next start clears in case AI Studio stops halfway:
+        var copyDirectory = Path.Join(DataRestoreFormat.DirectoryIn(dataDirectory, DataBackupFormat.STAGING_DIRECTORY), $"provenance-{Guid.NewGuid():N}");
+        try
+        {
+            var provenanceEntry = DataBackupContents.ENTRIES.First(entry => entry.Kind is DataBackupEntryKind.CHAT_PROVENANCE);
+            await provenanceStore.BackupToDirectoryAsync(Path.Join(copyDirectory, provenanceEntry.RelativePath.Replace(DataBackupContents.SEPARATOR, Path.DirectorySeparatorChar)), token);
+            return copyDirectory;
+        }
+        catch (OperationCanceledException) when (token.IsCancellationRequested)
+        {
+            this.TryDeleteCopies(copyDirectory);
+            throw;
+        }
+        catch (Exception exception)
+        {
+            logger.LogWarning(exception, "Copying the provenance store failed, so the backup takes it from the data folder as it lies there.");
+            this.TryDeleteCopies(copyDirectory);
+            return string.Empty;
+        }
+    }
+
     private DataBackupResult Refuse(string archivePath, string issue)
     {
         logger.LogWarning("Refused to start a backup into '{ArchivePath}': {Issue}", archivePath, issue);
@@ -291,21 +344,21 @@ public sealed class DataBackupService(ILogger<DataBackupService> logger, Setting
     }
 
     /// <summary>
-    /// Removes the copies of the indexes. Should that fail, the next start removes them.
+    /// Removes the copies a backup made of the indexes or of the provenance store. Should that fail, the next start removes them.
     /// </summary>
-    private void TryDeleteIndexCopies(string indexCopiesDirectory)
+    private void TryDeleteCopies(string copiesDirectory)
     {
-        if (string.IsNullOrWhiteSpace(indexCopiesDirectory))
+        if (string.IsNullOrWhiteSpace(copiesDirectory))
             return;
 
         try
         {
-            if (Directory.Exists(indexCopiesDirectory))
-                Directory.Delete(indexCopiesDirectory, true);
+            if (Directory.Exists(copiesDirectory))
+                Directory.Delete(copiesDirectory, true);
         }
         catch (Exception exception)
         {
-            logger.LogWarning(exception, "Could not remove the copies of the indexes at '{IndexCopiesDirectory}'.", indexCopiesDirectory);
+            logger.LogWarning(exception, "Could not remove the copies of the backup at '{CopiesDirectory}'.", copiesDirectory);
         }
     }
 }

app/MindWork AI Studio/Tools/Services/DataSourceEmbeddingService.Signature.cs

@@ -13,29 +13,42 @@ public sealed partial class DataSourceEmbeddingService
     internal const int DEFAULT_CHUNK_OVERLAP_TOKEN_LENGTH = 300;
 
     /// <summary>
-    /// What this build writes next to a chunk besides its text. Raise it whenever that changes.
+    /// The version of the chunk metadata, part of every embedding signature and frozen at 2. Raise it
+    /// only for a change which makes every stored vector wrong.
     /// </summary>
     /// <remarks>
-    /// A stored chunk keeps the metadata of the run which wrote it, and nothing recomputes it: the
-    /// fingerprint of a file says whether the file changed, not whether we got better at reading
-    /// it. Raising this number makes the embedding signature differ, which drops the index and
-    /// builds it again — the only way corrected page numbers reach a data source somebody indexed
-    /// earlier.
+    /// Raising this number makes the embedding signature of every data source differ, files and
+    /// mailboxes alike. That drops every index and sends every document to the embedding provider
+    /// once more, which is right only when no stored vector is valid anymore, e.g., because every
+    /// chunk would get another text. A better way of reading some files, or a new value stored next
+    /// to a chunk, does not justify it: a chunk which lacks the value reads as not knowing it, and
+    /// gains it once its document is indexed again.
     ///
     /// Version 2: the page of a chunk is taken from the runtime metadata instead of being read back
     /// out of the chunk text, which is what left Word and OpenDocument files, and passages
-    /// continuing across a page break, without a page.
+    /// continuing across a page break, without a page. It rebuilt every mailbox as well, although
+    /// mails have no pages, and fetched every mail from the server once more. That is why this
+    /// number is frozen.
+    ///
+    /// Not raised for the page a chunk ends on, which chunks store since v26.10.1. It adds to what
+    /// a chunk says and corrects nothing: a chunk without it still names its start page, which is
+    /// right, and gains its end page once its file is indexed again. Rebuilding every index for it
+    /// would send every document to the embedding provider once more, for a page range.
     /// </remarks>
     private const string CHUNK_METADATA_VERSION = "2";
 
     /// <summary>
-    /// What this build makes of a mail before it is cut into chunks. Raise it whenever that changes.
+    /// The version of what this build makes of a mail before it is cut into chunks, part of the
+    /// embedding signature of every mailbox and frozen at 2. Raise it only for a change which makes
+    /// every stored vector of a mailbox wrong.
     /// </summary>
     /// <remarks>
     /// The counterpart of CHUNK_METADATA_VERSION for mailboxes alone. A mail on the server never
     /// changes, so nothing reads it again once it is indexed, however differently MailTextBuilder
-    /// would write it today. Raising this number rebuilds the index of every mailbox and leaves
-    /// every other data source alone.
+    /// would write it today. Raising this number rebuilds the index of every mailbox, which fetches
+    /// every mail from the server and embeds it once more, and leaves every other data source alone.
+    /// A change which alters the text of some mails, such as those with attachments, does not
+    /// justify that.
     ///
     /// Version 1: the header block and the text from the HTML part, without attachments.
     ///

app/MindWork AI Studio/Tools/Services/DataSourceLocalRetrievalService.cs

@@ -1,9 +1,9 @@
 using AIStudio.Chat;
 using AIStudio.Settings;
 using AIStudio.Settings.DataModel;
+using AIStudio.Tools.Databases;
 using AIStudio.Tools.Databases.IndexStore;
 using AIStudio.Tools.Databases.VectorStore;
-using AIStudio.Tools.PluginSystem;
 using AIStudio.Tools.RAG;
 using AIStudio.Tools.Rust;
 
@@ -11,8 +11,6 @@ namespace AIStudio.Tools.Services;
 
 public sealed class DataSourceLocalRetrievalService(LocalIndexSearchService indexSearch, ILogger<DataSourceLocalRetrievalService> logger)
 {
-    private static string TB(string fallbackEN) => I18N.I.T(fallbackEN, typeof(DataSourceLocalRetrievalService).Namespace, nameof(DataSourceLocalRetrievalService));
-
     private enum RetrievalChannel
     {
         VECTOR,
@@ -36,7 +34,7 @@ public sealed class DataSourceLocalRetrievalService(LocalIndexSearchService inde
         string FileName,
         string RelativePath,
         string FileType,
-        int? PageNumber,
+        ChunkLocation Location,
         int ChunkIndex,
         string Text,
         double Score,
@@ -136,7 +134,7 @@ public sealed class DataSourceLocalRetrievalService(LocalIndexSearchService inde
             result.FileName,
             result.RelativePath,
             result.FileType,
-            result.PageNumber,
+            result.Location,
             result.ChunkIndex,
             result.Text,
             result.Score,
@@ -153,7 +151,7 @@ public sealed class DataSourceLocalRetrievalService(LocalIndexSearchService inde
             result.FileName,
             result.RelativePath,
             result.FileType,
-            result.PageNumber,
+            result.Location,
             result.ChunkIndex,
             result.ChunkText,
             result.Score,
@@ -164,36 +162,76 @@ public sealed class DataSourceLocalRetrievalService(LocalIndexSearchService inde
         var sourceName = FirstNonEmpty(hit.FileName, dataSource.Name);
         var path = FirstNonEmpty(hit.AbsolutePath, hit.RelativePath);
         var referenceLink = string.IsNullOrWhiteSpace(path) ? string.Empty : BuildReferenceLink(path, hit);
+        var type = GetRetrievalContentType(hit.FileType);
+        var located = LocatePassage(hit.Location, type, hit.ChunkIndex + 1);
 
         return new RetrievalTextContext
         {
             DataSourceName = sourceName,
             Category = RetrievalContentCategory.TEXT,
-            Type = GetRetrievalContentType(hit.FileType),
+            Type = type,
             Path = path,
             Links = [],
             MatchedText = hit.Text,
             SurroundingContent = [],
-            ReferenceTitle = BuildReferenceTitle(hit, dataSource),
+            ReferenceTitle = BuildReferenceTitle(sourceName, located),
             ReferenceLink = referenceLink,
-            PageNumber = hit.PageNumber is > 0 ? hit.PageNumber : null,
+            PageNumber = located.PageNumber,
+            EndPageNumber = located.EndPageNumber,
+            SheetName = located.SheetName,
+            StartRow = located.StartRow,
+            EndRow = located.EndRow,
+            StartLine = located.StartLine,
+            EndLine = located.EndLine,
+            ChunkNumber = located.ChunkNumber,
         };
     }
 
-    private static string BuildReferenceTitle(LocalRetrievalHit hit, IInternalDataSource dataSource)
+    /// <summary>
+    /// Where a hit is in its document, as its passage names it.
+    /// </summary>
+    /// <remarks>
+    /// An end only names a range when the passage goes on beyond where it starts. A chunk indexed
+    /// before an end, a row or a line was kept has none, and names what it has. The lines of a
+    /// table, such as a CSV file, are its rows. A transcript names no lines: it is a file the user
+    /// never sees, so its lines would point nowhere.
+    /// </remarks>
+    /// <param name="location">Where the chunk of the hit is.</param>
+    /// <param name="type">What kind of content the hit is.</param>
+    /// <param name="chunkNumber">Which part of its document the hit is, counted from one.</param>
+    /// <returns>A passage holding nothing but where the hit is.</returns>
+    internal static SourcePassage LocatePassage(ChunkLocation location, RetrievalContentType type, int chunkNumber)
     {
-        var sourceName = FirstNonEmpty(hit.FileName, dataSource.Name);
-        return BuildLocatedReferenceTitle(sourceName, hit.ChunkIndex, hit.PageNumber);
+        var pageNumber = location.PageNumber is > 0 ? location.PageNumber : null;
+        var rows = RangeOf(location.StartRow, location.EndRow);
+        var lines = type is RetrievalContentType.TEXT_TRANSCRIPT ? PassageRange.NONE : RangeOf(location.StartLine, location.EndLine);
+        if (type is RetrievalContentType.TEXT_SPREADSHEET && rows.Start is null)
+        {
+            rows = lines;
+            lines = PassageRange.NONE;
+        }
+
+        return new SourcePassage
+        {
+            Type = type,
+            PageNumber = pageNumber,
+            EndPageNumber = pageNumber is not null && location.EndPageNumber > pageNumber ? location.EndPageNumber : null,
+            SheetName = rows.Start is null ? null : location.SheetName,
+            StartRow = rows.Start,
+            EndRow = rows.End,
+            StartLine = lines.Start,
+            EndLine = lines.End,
+            ChunkNumber = chunkNumber,
+        };
     }
 
-    private static string BuildLocatedReferenceTitle(string sourceName, int chunkIndex, int? pageNumber)
-    {
-        var location = pageNumber is > 0
-            ? string.Format(TB("Page {0}"), pageNumber)
-            : string.Format(TB("Chunk {0}"), chunkIndex + 1);
+    private static PassageRange RangeOf(int? start, int? end) => start is > 0 ? new(start, end > start ? end : null) : PassageRange.NONE;
 
-        return $"{sourceName} ({location})";
-    }
+    //
+    // Worded like the location of every passage, so that the title reads the same before and after
+    // the passages of an answer rename it, cf. SourcePassageExtensions.NamePassagesInTitles:
+    //
+    private static string BuildReferenceTitle(string sourceName, SourcePassage located) => $"{sourceName} ({located.GetLocationLabel()})";
 
     /// <remarks>
     /// A known page is written as the fragment `#page=N`, which is what the PDF open parameters
@@ -205,8 +243,8 @@ public sealed class DataSourceLocalRetrievalService(LocalIndexSearchService inde
     {
         var link = NormalizeLocalReferencePath(path);
         var separator = link.Contains('#', StringComparison.Ordinal) ? "&" : "#";
-        return hit.PageNumber is > 0
-            ? $"{link}{separator}page={hit.PageNumber}"
+        return hit.Location.PageNumber is > 0
+            ? $"{link}{separator}page={hit.Location.PageNumber}"
             : $"{link}{separator}chunk={hit.ChunkIndex}";
     }
 
@@ -224,8 +262,12 @@ public sealed class DataSourceLocalRetrievalService(LocalIndexSearchService inde
         }
     }
 
-    private static RetrievalContentType GetRetrievalContentType(string fileType)
+    internal static RetrievalContentType GetRetrievalContentType(string fileType)
     {
+        // An audio or a video file is indexed by its transcript, so that is what its passages are:
+        if (FileTypes.IsAllowedExtension(fileType, FileTypes.AUDIO, FileTypes.VIDEO))
+            return RetrievalContentType.TEXT_TRANSCRIPT;
+
         if (FileTypes.IsAllowedExtension(fileType, FileTypes.TABULAR, FileTypes.SPREADSHEET))
             return RetrievalContentType.TEXT_SPREADSHEET;
 
@@ -266,7 +308,7 @@ public sealed class DataSourceLocalRetrievalService(LocalIndexSearchService inde
                 result.Result.ParentFileId,
                 result.Result.FileName,
                 FirstNonEmpty(result.Result.AbsolutePath, result.Result.FilePath),
-                BuildLocatedReferenceTitle(FirstNonEmpty(result.Result.FileName, dataSource.Name), result.Result.ChunkIndex, result.Result.PageNumber));
+                BuildReferenceTitle(FirstNonEmpty(result.Result.FileName, dataSource.Name), LocatePassage(result.Result.Location, GetRetrievalContentType(result.Result.FileType), result.Result.ChunkIndex + 1)));
         }
     }
 
@@ -290,7 +332,7 @@ public sealed class DataSourceLocalRetrievalService(LocalIndexSearchService inde
                 result.Result.ParentFileId,
                 result.Result.FileName,
                 result.Result.AbsolutePath,
-                BuildLocatedReferenceTitle(FirstNonEmpty(result.Result.FileName, dataSource.Name), result.Result.ChunkIndex, result.Result.PageNumber));
+                BuildReferenceTitle(FirstNonEmpty(result.Result.FileName, dataSource.Name), LocatePassage(result.Result.Location, GetRetrievalContentType(result.Result.FileType), result.Result.ChunkIndex + 1)));
         }
     }
 }

app/MindWork AI Studio/Tools/Services/EmbeddedFileRecord.cs

@@ -1,4 +1,4 @@
 namespace AIStudio.Tools.Services;
 
 public sealed record EmbeddedFileRecord(string Fingerprint, long FileSize, DateTimeOffset LastWriteUtc, DateTimeOffset EmbeddedAtUtc, int ChunkCount, string? TranscriptKey = null,
-    string? RelativePath = null, string? ParentFileId = null);
+    string? RelativePath = null, string? ParentFileId = null, string? ContentHash = null, int Generation = 0);

app/MindWork AI Studio/Tools/Services/Indexing/AGENTS.md

@@ -15,10 +15,24 @@ The parts:
 - **`IIndexedSourceIndexer`** - one per kind of data source. `Supports` claims the data sources, `ProcessAsync`
   finds and reads the documents of one run, and `TrackChanges` / `StopTracking` notice changes on their own.
   `FileSourceIndexer` is the reference: a file system watcher per data source, fingerprints over path, size and
-  write time.
+  write time, and once a fingerprint changed, the hash of the content (`FileContentHash`), so a file saved again
+  without edits keeps its chunks without being read.
 - **`IndexedRunContext`** - one prepared run: both stores, the embedding provider, the manifest, the
-  collection, and the scope for reporting prompt injections. `IndexDocumentAsync` embeds and stores one
-  document; the cleanup methods remove what a failed attempt left behind.
+  collection, and the scope for reporting prompt injections. `IndexDocumentAsync` embeds one document into a
+  new generation, next to the version it had stored; `DocumentRunProgress.RecordDocumentIndexedAsync` completes
+  it (`CompleteDocumentAsync`), and `CleanupFailedDocumentAsync` sorts out a failed attempt. A document indexed
+  before keeps its stored version whatever the failure, so never remove its manifest entry on a failure. Once
+  the embedding provider fails, the attempt asks it nothing more and reads the rest of the document for the
+  chunks with a stored vector; a document with nothing stored stops at the failure, since none of its chunks
+  could take over a vector. Either way, the attempt stays next to the stored version, so the next one reuses
+  its vectors; one which stopped for any other reason goes. Between attempts, a document keeps two generations at
+  most: the one its row names, and an attempt which stays for its vectors. A run of the file indexer removes the
+  others of every file which did not change since (`IndexedRunContext.RemoveLeftoverGenerationsAsync`), since no
+  attempt would ever come for it. A chunk whose text the document had stored before keeps its vector (`ReusableVectors`),
+  found by the hash of exactly the text that goes to the embedding provider (`ChunkTextHash`), so hash whatever
+  is sent, and send whatever is stored. The new chunks belong to the next generation, which is part of their
+  ids (`IndexedDocumentIds.CreateChunkIdSource`), so they never overwrite an old chunk, not even for a mail,
+  whose fingerprint never changes.
 - **`EmbeddingDocument`** - one document: its key, its index row, its display name, and how to read its chunks.
 - **`DocumentRunProgress`** - counts the documents, records indexed and failed ones in the stores, publishes the
   status, and completes or pauses the run.
@@ -30,7 +44,9 @@ The parts:
   which documents failed during an earlier step, so the next steps do not read them again, and which failures
   were reported to the user already.
 - **`TextChunker`** - cuts text into chunks the embedding provider accepts. Pick one of its strategies; do not
-  write a chunker of your own.
+  write a chunker of your own. It also says where each chunk starts and ends (`SourceLocation`: page, sheet and
+  row, or line), from the segments the runtime delivered; never read a location back out of the chunk text.
+  Only the pages go into the vector store, everything else about a location into the index store alone.
 
 To add a kind of data source:
 1. Write its indexer in `Tools/Services/Indexing/` and create it in `DataSourceEmbeddingService.CreateIndexers`,
@@ -59,8 +75,17 @@ Rules which are easy to break:
   `Path` APIs: on Windows, `Path.GetFullPath` reads a key like `mail:…` as a file with an alternate data stream.
 - **Ids and signature are pinned.** The formats in `IndexedDocumentIds` and the embedding signature
   (`DataSourceEmbeddingService.BuildEmbeddingSignature`) are fixed by tests, because every stored chunk and every
-  index depends on them. When the metadata stored next to a chunk changes, raise `CHUNK_METADATA_VERSION`
-  deliberately: that rebuilds every index.
+  index depends on them. `CHUNK_METADATA_VERSION` and `MAIL_TEXT_VERSION` are frozen: raising one rebuilds every
+  index it is part of, so raise it only when every stored vector is wrong. A change to how documents are read, or
+  to what is stored next to a chunk, raises neither. A new value which old chunks may lack without being wrong,
+  such as the end page of a chunk, reads as unknown, and a chunk gains it once its document is indexed again.
+- **A search finds the generation the row of a document names, and nothing else.** A row whose chunk count is
+  zero names none yet. The keyword search joins on it (`SqliteIndexStoreClientImplementation.MatchChunks`), and
+  the vector search leaves out `IndexStoreClient.GetHiddenChunksAsync`, which the runtime matches against the
+  `generation` of every point. A new way to search the index, or to list chunks for a search, follows the same
+  rule, or it finds failed attempts and documents which are not complete. Write a chunk into the index store
+  before its point into the vector store, and remove the point before the chunk: a point the index store does
+  not know cannot be hidden.
 - **The service decides when, the indexer decides how.** Whether changes are tracked at all depends on the
   automatic refresh setting and the startup hash check, and only the embedding service decides that.
 - **A pause stores the source hash only when a partial index may be searched.** A stored source hash tells the

app/MindWork AI Studio/Tools/Services/Indexing/ChunkSpan.cs

@@ -0,0 +1,8 @@
+namespace AIStudio.Tools.Services.Indexing;
+
+/// <summary>
+/// Where a chunk starts and where it ends in its document, cf. TextChunker.Locate.
+/// </summary>
+/// <param name="Start">Where the chunk starts.</param>
+/// <param name="End">Where the chunk ends.</param>
+internal readonly record struct ChunkSpan(SourceLocation Start, SourceLocation End);

app/MindWork AI Studio/Tools/Services/Indexing/DocumentRunProgress.cs

@@ -215,22 +215,21 @@ internal sealed class DocumentRunProgress(IndexedRunContext context, int totalDo
     /// </summary>
     /// <remarks>
     /// Called once the kind of data source is sure the document did not change while it was read.
-    /// Until then, its index row says it has no chunks.
+    /// Until then, the document keeps the version it had, or its index row says it has no chunks
+    /// when it is new.<br/><br/>
+    /// The row names the new generation first, which every search goes by from then on, and only
+    /// then do the other generations go. A crash in between leaves chunks which no search finds,
+    /// and which the next indexing of the document removes.
     /// </remarks>
     /// <param name="document">The document.</param>
-    /// <param name="chunkCount">How many chunks were stored for it.</param>
+    /// <param name="indexed">What indexing the document stored.</param>
     /// <param name="isNew">Whether the index knew nothing about it before.</param>
     /// <param name="token">The cancellation token.</param>
-    public async Task RecordDocumentIndexedAsync(EmbeddingDocument document, int chunkCount, bool isNew, CancellationToken token)
+    public async Task RecordDocumentIndexedAsync(EmbeddingDocument document, IndexedDocument indexed, bool isNew, CancellationToken token)
     {
-        var embeddedAtUtc = DateTimeOffset.UtcNow;
-        var state = document.State with { ChunkCount = chunkCount, EmbeddedAtUtc = embeddedAtUtc };
-        await context.IndexStore.UpsertFileAsync(context.DataSource.Id, state, token);
-        context.Manifest.Files[document.Key] = new EmbeddedFileRecord(state.Fingerprint, state.FileSize, state.LastWriteUtc, embeddedAtUtc, chunkCount, state.TranscriptKey, state.RelativePath, state.ParentFileId);
-        await context.ForgetPermanentFailureAsync(document.Key, token);
-        context.Pass.Forget(document.Key);
+        await this.StoreDocumentStateAsync(document.Key, document.State with { ChunkCount = indexed.ChunkCount, Generation = indexed.Generation, EmbeddedAtUtc = DateTimeOffset.UtcNow }, token);
+        await context.CompleteDocumentAsync(document.Key, indexed, token);
 
-        this.readDocuments++;
         this.IndexedDocuments++;
         if (isNew)
             this.NewDocuments++;
@@ -238,10 +237,54 @@ internal sealed class DocumentRunProgress(IndexedRunContext context, int totalDo
             this.ChangedDocuments++;
     }
 
+    /// <summary>
+    /// Records a document whose fingerprint changed while its content did not, e.g., a file saved again without edits.
+    /// </summary>
+    /// <remarks>
+    /// Its chunks and vectors stay as they are, under the ids they have. Only the new fingerprint
+    /// is written, into the vector store as well as into the index store, the way a relocation
+    /// writes it, so the next run finds the document unchanged. Nothing is read through the
+    /// runtime, and nothing goes to the embedding provider. An attempt which failed in between and
+    /// stays for its vectors is of no use any longer, and goes.
+    /// </remarks>
+    /// <param name="document">The document, as it would be indexed now.</param>
+    /// <param name="storedRecord">What the manifest knows about the document from its last indexing.</param>
+    /// <param name="token">The cancellation token.</param>
+    public async Task RecordContentUnchangedAsync(EmbeddingDocument document, EmbeddedFileRecord storedRecord, CancellationToken token)
+    {
+        var state = document.State with { ChunkCount = storedRecord.ChunkCount, EmbeddedAtUtc = storedRecord.EmbeddedAtUtc, TranscriptKey = storedRecord.TranscriptKey, Generation = storedRecord.Generation };
+        await context.VectorStore.RelocateEmbeddingFileAsync(context.CollectionName, state.ParentFileId, state.AbsolutePath, state.RelativePath, state.Fingerprint, token);
+        token.ThrowIfCancellationRequested();
+        await this.StoreDocumentStateAsync(document.Key, state, token);
+        await context.KeepOnlyGenerationAsync(document.Key, storedRecord.Generation, token);
+
+        this.UnchangedDocuments++;
+    }
+
+    /// <summary>
+    /// Writes the row of a document which is in the index from now on, and what the manifest knows about it.
+    /// </summary>
+    /// <param name="documentKey">The key of the document.</param>
+    /// <param name="state">The row.</param>
+    /// <param name="token">The cancellation token.</param>
+    private async Task StoreDocumentStateAsync(string documentKey, EmbeddingStateFile state, CancellationToken token)
+    {
+        await context.IndexStore.UpsertFileAsync(context.DataSource.Id, state, token);
+        context.Manifest.Files[documentKey] = new EmbeddedFileRecord(state.Fingerprint, state.FileSize, state.LastWriteUtc, state.EmbeddedAtUtc, state.ChunkCount, state.TranscriptKey, state.RelativePath, state.ParentFileId, state.ContentHash, state.Generation);
+        context.Manifest.UnfinishedFiles.Remove(documentKey);
+        await context.ForgetPermanentFailureAsync(documentKey, token);
+        context.Pass.Forget(documentKey);
+
+        this.readDocuments++;
+    }
+
     /// <summary>
     /// Records why a document could not be indexed, and removes what the attempt left behind.
     /// </summary>
     /// <remarks>
+    /// A document indexed before keeps the version it had, whatever the failure, cf.
+    /// IndexedRunContext.CleanupFailedDocumentAsync. So it stays in the manifest, with the
+    /// fingerprint of that version, and the next run tries it again once the pass allows.<br/><br/>
     /// Never called for a cancelled run, nor for a vector store which cannot be read at all: those
     /// are not about one document, and whoever indexes has to let them through.
     /// </remarks>
@@ -269,7 +312,6 @@ internal sealed class DocumentRunProgress(IndexedRunContext context, int totalDo
                 var failure = new DataSourceEmbeddingFailure(document.Key, providerFailure.UserMessage, DateTimeOffset.UtcNow, providerFailure.FailureReason, providerFailure.StatusCode, context.EmbeddingProvider.Name, DisplayName: document.DisplayName);
                 this.failures.Add(failure);
                 context.Pass.RecordFailure(document.Key, document.State.Fingerprint, failure);
-                context.Manifest.Files.Remove(document.Key);
                 await context.ForgetPermanentFailureAsync(document.Key, token);
                 await context.CleanupFailedDocumentAsync(document.Key, token);
 
@@ -297,12 +339,12 @@ internal sealed class DocumentRunProgress(IndexedRunContext context, int totalDo
                 // the document does. The reason is written into the index, and the fingerprint next
                 // to it decides when to come back: an OCR run over a scanned PDF changes both size
                 // and write time, which is exactly the moment the file deserves another attempt.
+                // Meanwhile, a file indexed before can still be found by its last good version.
                 //
                 this.PermanentlySkippedDocuments++;
                 var occurredAtUtc = DateTimeOffset.UtcNow;
                 var indexingMessage = this.GetFailureMessage(extractionFailure.Code, document, extractionFailure.Message);
                 this.failures.Add(new DataSourceEmbeddingFailure(document.Key, indexingMessage, occurredAtUtc, ExtractionCode: extractionFailure.Code, IsPermanent: true, DisplayName: document.DisplayName));
-                context.Manifest.Files.Remove(document.Key);
                 context.Pass.Forget(document.Key);
                 await context.CleanupFailedDocumentAsync(document.Key, token);
 
@@ -346,7 +388,6 @@ internal sealed class DocumentRunProgress(IndexedRunContext context, int totalDo
                 var failure = new DataSourceEmbeddingFailure(document.Key, failureMessage, DateTimeOffset.UtcNow, EmbeddingProviderName: context.EmbeddingProvider.Name, ExtractionCode: extractionCode, DisplayName: document.DisplayName);
                 this.failures.Add(failure);
                 context.Pass.RecordFailure(document.Key, document.State.Fingerprint, failure);
-                context.Manifest.Files.Remove(document.Key);
                 await context.ForgetPermanentFailureAsync(document.Key, token);
                 await context.CleanupFailedDocumentAsync(document.Key, token);
 

app/MindWork AI Studio/Tools/Services/Indexing/EmbeddingChunk.cs

@@ -1,14 +1,27 @@
 namespace AIStudio.Tools.Services.Indexing;
 
 /// <summary>
-/// One chunk as the chunking produced it, together with the page it starts on.
+/// One chunk as the chunking produced it, together with where it starts and where it ends.
 /// </summary>
 /// <remarks>
-/// The page is carried rather than read back out of the chunk text. The runtime states it, and
-/// the chunking knows which source segment a chunk begins in, so nothing has to be derived from
-/// a marker in the text — which is what used to leave Word files and continued passages without
-/// a page.
+/// The locations are carried rather than read back out of the chunk text. The runtime states them,
+/// and the chunking knows which source segments a chunk covers, so nothing has to be derived from a
+/// marker in the text — which is what used to leave Word files and continued passages without a
+/// page.
 /// </remarks>
 /// <param name="Text">The chunk itself, overlap prefix included.</param>
-/// <param name="PageNumber">The page the chunk's own content starts on, or null when it has none.</param>
-internal sealed record EmbeddingChunk(string Text, int? PageNumber);
+/// <param name="Start">Where the chunk's own content starts: its page, its sheet and row, or its line.</param>
+/// <param name="End">Where the chunk ends. Equal to the start when the chunk stays within one page, row or line.</param>
+/// <param name="AttachmentPosition">Which attachment of a mail the chunk is from, counted from zero as the index numbers them, or null for the text of the mail itself and for anything but a mail.</param>
+internal sealed record EmbeddingChunk(string Text, SourceLocation Start, SourceLocation End, int? AttachmentPosition = null)
+{
+    /// <summary>
+    /// The page the chunk's own content starts on, or null when it has none.
+    /// </summary>
+    public int? PageNumber => this.Start.PageNumber;
+
+    /// <summary>
+    /// The page the chunk ends on, or null when it has none.
+    /// </summary>
+    public int? EndPageNumber => this.End.PageNumber;
+}

app/MindWork AI Studio/Tools/Services/Indexing/ExtractedFileText.cs

@@ -29,7 +29,7 @@ internal static class ExtractedFileText
         {
             var normalized = TextChunker.NormalizeSegment(segment.Content);
             if (!string.IsNullOrWhiteSpace(normalized))
-                segments.Add(new(normalized, segment.TokenCount, segment.PageNumber));
+                segments.Add(new(normalized, segment.TokenCount, segment.Location));
         }
 
         return new(string.Join("\n", segments.Select(segment => segment.Text)).Trim(), segments);

app/MindWork AI Studio/Tools/Services/Indexing/FileSourceIndexer.cs

@@ -129,6 +129,9 @@ internal sealed partial class FileSourceIndexer(SettingsManager settingsManager,
         var removedMissingFiles = await this.RemoveMissingFileEmbeddingsAsync(context, inputFiles, token);
         token.ThrowIfCancellationRequested();
 
+        // Before the data source may be skipped as unchanged, since nothing else removes what is left of an unchanged file:
+        await context.RemoveLeftoverGenerationsAsync(key => manifest.Files.TryGetValue(key, out var record) && metadataSnapshot.FileHashes.TryGetValue(key, out var fingerprint) && string.Equals(record.Fingerprint, fingerprint, StringComparison.Ordinal), token);
+
         logger.LogInformation(
             "Compared data source hash for '{DataSourceName}' ({DataSourceId}). StoredSourceHashPrefix={StoredSourceHashPrefix}, CurrentSourceHashPrefix={CurrentSourceHashPrefix}, StoredFileRecords={StoredFileRecords}, CurrentFiles={CurrentFiles}, RemovedMissingFiles={RemovedMissingFiles}.",
             dataSource.Name,
@@ -213,6 +216,29 @@ internal sealed partial class FileSourceIndexer(SettingsManager settingsManager,
 
             try
             {
+                //
+                // The fingerprint changed, but perhaps not the content: a file saved again without
+                // edits, synchronized or copied keeps its chunks and vectors, and only its new
+                // fingerprint is stored. Reading the bytes once costs far less than extracting and
+                // embedding them again. The transcript of an audio or video file is filed under the
+                // same hash, so a recording indexed before this hash was kept is recognized as well.
+                //
+                var contentHash = await FileContentHash.ComputeAsync(file.FullName, token);
+                document = this.CreateFileDocument(context, dataSource, file, fingerprint, null, contentHash);
+                if (existingRecord is { ParentFileId: not null } && string.Equals(existingRecord.ContentHash ?? existingRecord.TranscriptKey, contentHash, StringComparison.Ordinal))
+                {
+                    await progress.RecordContentUnchangedAsync(document, existingRecord, token);
+                    logger.LogInformation(
+                        "Kept the stored chunks of file '{FilePath}' for data source '{DataSourceName}' ({DataSourceId}) without reading it, because its content did not change, although {EmbeddingReason}. Progress={CompletedFiles}/{TotalFiles}.",
+                        file.FullName,
+                        dataSource.Name,
+                        dataSource.Id,
+                        GetFileEmbeddingReason(file, fingerprint, existingRecord),
+                        progress.DoneDocuments,
+                        totalFiles);
+                    continue;
+                }
+
                 logger.LogInformation(
                     "Embedding file '{FilePath}' for data source '{DataSourceName}' ({DataSourceId}) because {EmbeddingReason}. CurrentMetadataHashPrefix={CurrentMetadataHashPrefix}. Progress={CompletedFiles}/{TotalFiles}.",
                     file.FullName,
@@ -228,15 +254,15 @@ internal sealed partial class FileSourceIndexer(SettingsManager settingsManager,
                 // its transcript instead, and its row knows which transcript that is:
                 //
                 if (PersistentMediaTranscript.IsMediaPath(file.FullName))
-                    document = this.CreateFileDocument(context, dataSource, file, fingerprint, await this.ReadOrCreateTranscriptAsync(dataSource, file.FullName, token));
+                    document = this.CreateFileDocument(context, dataSource, file, fingerprint, await this.ReadOrCreateTranscriptAsync(dataSource, file.FullName, contentHash, fingerprint, token), contentHash);
 
-                var chunkCount = await context.IndexDocumentAsync(document, reportBlockProgress, token);
+                var indexed = await context.IndexDocumentAsync(document, reportBlockProgress, token);
                 token.ThrowIfCancellationRequested();
                 var fingerprintAfterEmbedding = BuildFileMetadataHash(file);
                 if (!string.Equals(fingerprint, fingerprintAfterEmbedding, StringComparison.Ordinal))
                     throw new IOException(string.Format(TB("The file '{0}' changed while it was being indexed. What was indexed of it is discarded, and the file is tried again during the next run."), file.FullName));
 
-                await progress.RecordDocumentIndexedAsync(document, chunkCount, existingRecord is null, token);
+                await progress.RecordDocumentIndexedAsync(document, indexed, existingRecord is null, token);
 
                 // The recording changed, so its old transcript is no longer what it says:
                 if (existingRecord?.TranscriptKey is { } previousTranscriptKey && !string.Equals(previousTranscriptKey, document.State.TranscriptKey, StringComparison.Ordinal))
@@ -247,7 +273,7 @@ internal sealed partial class FileSourceIndexer(SettingsManager settingsManager,
                     file.FullName,
                     dataSource.Name,
                     dataSource.Id,
-                    chunkCount,
+                    indexed.ChunkCount,
                     (DateTimeOffset.UtcNow - startedAtUtc).TotalMilliseconds);
             }
             catch (OperationCanceledException) when (token.IsCancellationRequested)
@@ -552,14 +578,16 @@ internal sealed partial class FileSourceIndexer(SettingsManager settingsManager,
     /// <remarks>
     /// A file counts as settled when it was indexed or when it was skipped for good, both with a
     /// matching fingerprint. Counting only the indexed ones would let a single unreadable document
-    /// send the whole folder through the slow path on every run.
+    /// send the whole folder through the slow path on every run. A file which was indexed before
+    /// and then failed for good keeps its stored version, so it is in both lists: it counts once,
+    /// as settled by its failure.
     /// </remarks>
     private static bool CanSkipDataSourceByHash(DataSourceEmbeddingManifest manifest, DataSourceMetadataSnapshot metadataSnapshot, IReadOnlyCollection<FileInfo> indexedFiles)
     {
         if (!string.Equals(manifest.SourceHash, metadataSnapshot.SourceHash, StringComparison.Ordinal))
             return false;
 
-        if (manifest.Files.Count + manifest.PermanentFailures.Count != indexedFiles.Count)
+        if (manifest.Files.Keys.Union(manifest.PermanentFailures.Keys, DataSourceEmbeddingManifest.PATH_COMPARER).Count() != indexedFiles.Count)
             return false;
 
         foreach (var file in indexedFiles)
@@ -567,18 +595,9 @@ internal sealed partial class FileSourceIndexer(SettingsManager settingsManager,
             if (!metadataSnapshot.FileHashes.TryGetValue(file.FullName, out var currentHash))
                 return false;
 
-            if (manifest.Files.TryGetValue(file.FullName, out var existingRecord))
-            {
-                if (!string.Equals(existingRecord.Fingerprint, currentHash, StringComparison.Ordinal))
-                    return false;
-
-                continue;
-            }
-
-            if (!manifest.PermanentFailures.TryGetValue(file.FullName, out var permanentFailure))
-                return false;
-
-            if (!string.Equals(permanentFailure.Fingerprint, currentHash, StringComparison.Ordinal))
+            var isIndexed = manifest.Files.TryGetValue(file.FullName, out var existingRecord) && string.Equals(existingRecord.Fingerprint, currentHash, StringComparison.Ordinal);
+            var isUnreadable = manifest.PermanentFailures.TryGetValue(file.FullName, out var permanentFailure) && string.Equals(permanentFailure.Fingerprint, currentHash, StringComparison.Ordinal);
+            if (!isIndexed && !isUnreadable)
                 return false;
         }
 
@@ -636,12 +655,17 @@ internal sealed partial class FileSourceIndexer(SettingsManager settingsManager,
     /// </remarks>
     /// <param name="dataSource">The data source.</param>
     /// <param name="mediaPath">The audio or video file.</param>
+    /// <param name="contentHash">The hash of its content, cf. FileContentHash.</param>
+    /// <param name="fingerprint">Its fingerprint, taken before its content was hashed.</param>
     /// <param name="token">The cancellation token.</param>
     /// <returns>Where the transcript is.</returns>
-    private async Task<MediaTranscriptSlot> ReadOrCreateTranscriptAsync(IDataSource dataSource, string mediaPath, CancellationToken token)
+    private async Task<MediaTranscriptSlot> ReadOrCreateTranscriptAsync(IDataSource dataSource, string mediaPath, string contentHash, string fingerprint, CancellationToken token)
     {
         var provider = this.GetMediaTranscriptionAvailability(dataSource).Provider;
-        var transcript = await PersistentMediaTranscript.ReadOrCreateAsync(DataSourceTranscriptStore.ForDataSource(dataSource.Id), mediaPath, provider, mediaTranscriptionService.TranscribeAsync, logger, token);
+
+        // The content was hashed under the fingerprint taken before, so the store need not read the whole recording again:
+        var location = DataSourceTranscriptStore.ForDataSource(dataSource.Id).WithKnownContentHash(contentHash, path => string.Equals(BuildFileMetadataHash(new FileInfo(path)), fingerprint, StringComparison.Ordinal));
+        var transcript = await PersistentMediaTranscript.ReadOrCreateAsync(location, mediaPath, provider, mediaTranscriptionService.TranscribeAsync, logger, token);
         return GetTranscriptOrThrow(transcript, token);
     }
 
@@ -1060,10 +1084,11 @@ internal sealed partial class FileSourceIndexer(SettingsManager settingsManager,
     /// <param name="file">The file.</param>
     /// <param name="fingerprint">The fingerprint of the file as it is about to be read.</param>
     /// <param name="transcript">The transcript an audio or video file is read through, or null for every other file.</param>
+    /// <param name="contentHash">The hash of the content of the file, cf. FileContentHash, or null while it is not computed yet.</param>
     /// <returns>The document.</returns>
-    private EmbeddingDocument CreateFileDocument(IndexedRunContext context, IDataSource dataSource, FileInfo file, string fingerprint, MediaTranscriptSlot? transcript) => new(
+    private EmbeddingDocument CreateFileDocument(IndexedRunContext context, IDataSource dataSource, FileInfo file, string fingerprint, MediaTranscriptSlot? transcript, string? contentHash = null) => new(
         file.FullName,
-        this.CreateEmbeddingStateFile(dataSource, file, fingerprint, 0, DateTimeOffset.UtcNow) with { ParentFileId = context.GetFileParentId(file.FullName), TranscriptKey = transcript?.Key },
+        this.CreateEmbeddingStateFile(dataSource, file, fingerprint, 0, DateTimeOffset.UtcNow) with { ParentFileId = context.GetFileParentId(file.FullName), TranscriptKey = transcript?.Key, ContentHash = contentHash },
         file.Name,
         token => this.StreamEmbeddingChunksAsync(file.FullName, transcript, dataSource, context.EmbeddingProvider, context.PromptInjectionScope, token));
 

app/MindWork AI Studio/Tools/Services/Indexing/IndexedDocument.cs

@@ -0,0 +1,14 @@
+namespace AIStudio.Tools.Services.Indexing;
+
+/// <summary>
+/// What indexing a document stored: a new generation of its chunks, next to whatever the document had before.
+/// </summary>
+/// <remarks>
+/// The new generation replaces the stored one only once the kind of data source records the
+/// document as indexed, cf. DocumentRunProgress.RecordDocumentIndexedAsync. Until then, and for
+/// good when it fails, the document keeps the version it had.
+/// </remarks>
+/// <param name="ChunkCount">How many chunks were stored.</param>
+/// <param name="Generation">The generation of the chunks, cf. IndexedDocumentIds.CreateChunkIdSource.</param>
+/// <param name="ChunkIds">The ids of the chunks, which are also the ids of their points.</param>
+internal sealed record IndexedDocument(int ChunkCount, int Generation, IReadOnlyList<string> ChunkIds);

app/MindWork AI Studio/Tools/Services/Indexing/IndexedDocumentIds.cs

@@ -26,25 +26,35 @@ internal static class IndexedDocumentIds
         CreateStableGuid($"{dataSourceId}:chunk:{source}:{chunkIndex}");
 
     /// <summary>
-    /// What the chunk ids of a document derive from: nearly always its fingerprint.
+    /// What the chunk ids of a document derive from: nearly always its fingerprint, and the generation of the chunks.
     /// </summary>
     /// <remarks>
     /// A moved file keeps its parent id and its chunk ids, but its fingerprint now names the new path.
     /// Another file may later appear at the old path with exactly the fingerprint those chunk ids came
     /// from, and the fingerprint alone would hand it the same ids. The two documents would then take
     /// over each other's chunks. Hence the parent id joins whenever a document is not stored under the
-    /// id its key gives, which only happens after a move. Every other document keeps the ids it has.
+    /// id its key gives, which only happens after a move. Every other document keeps the ids it has.<br/><br/>
+    /// Every time a document is indexed again, its chunks get the next generation, and with it new
+    /// ids, even where the fingerprint stays the same, as for a mail. So the new chunks never
+    /// overwrite the old ones, which keep their vectors until the new chunks are stored, cf.
+    /// ReusableVectors. The first indexing of a document is generation 0, which gives the ids
+    /// documents got before generations existed.
     /// </remarks>
     /// <param name="dataSourceId">The data source the document belongs to.</param>
     /// <param name="documentKey">The key of the document.</param>
     /// <param name="parentId">The id the document is stored under.</param>
     /// <param name="fingerprint">The fingerprint of the document as it is about to be read.</param>
+    /// <param name="generation">The generation of the chunks about to be written.</param>
     /// <returns>What to pass to CreateChunkId.</returns>
-    public static string CreateChunkIdSource(string dataSourceId, string documentKey, string parentId, string fingerprint) =>
-        string.Equals(parentId, CreateParentId(dataSourceId, documentKey), StringComparison.Ordinal)
+    public static string CreateChunkIdSource(string dataSourceId, string documentKey, string parentId, string fingerprint, int generation = 0)
+    {
+        var source = string.Equals(parentId, CreateParentId(dataSourceId, documentKey), StringComparison.Ordinal)
             ? fingerprint
             : $"{parentId}:{fingerprint}";
 
+        return generation is 0 ? source : $"{source}:generation:{generation}";
+    }
+
     /// <summary>
     /// The id of a document's row in the index store, which its chunks point at.
     /// </summary>

app/MindWork AI Studio/Tools/Services/Indexing/IndexedRunContext.cs

@@ -1,3 +1,5 @@
+using System.Runtime.ExceptionServices;
+
 using AIStudio.Provider;
 using AIStudio.Settings;
 using AIStudio.Tools.Databases.IndexStore;
@@ -44,12 +46,45 @@ internal sealed class IndexedRunContext(IIndexedDataSource dataSource, Embedding
     private Dictionary<string, string>? fileParentIds;
     private HashSet<string>? reservedFileParentIds;
 
+    private readonly Dictionary<string, IndexingAttempt> attempts = new(DataSourceEmbeddingManifest.PATH_COMPARER);
+
     private static string TB(string fallbackEN) => I18N.I.T(fallbackEN, typeof(IndexedRunContext).Namespace, nameof(IndexedRunContext));
 
     /// <summary>
-    /// One chunk on its way to the stores, with the id it is stored under.
+    /// One chunk on its way to the stores, with the id it is stored under and the hash of its text.
     /// </summary>
-    private sealed record EmbeddingChunkDraft(string ChunkId, string Text, int ChunkIndex, int? PageNumber);
+    private sealed record EmbeddingChunkDraft(string ChunkId, EmbeddingChunk Chunk, string TextHash, int ChunkIndex)
+    {
+        public string Text => this.Chunk.Text;
+    }
+
+    /// <summary>
+    /// One attempt to index a document, from reading what it had stored until it is completed or cleaned up.
+    /// </summary>
+    /// <param name="generation">The generation the attempt writes.</param>
+    /// <param name="earlierGenerations">The generations the document had stored when the attempt began.</param>
+    private sealed class IndexingAttempt(int generation, IReadOnlyCollection<int> earlierGenerations)
+    {
+        public int Generation => generation;
+
+        public IReadOnlyCollection<int> EarlierGenerations => earlierGenerations;
+
+        /// <summary>
+        /// The first failure of the embedding provider, after which the attempt asks it nothing more.
+        /// </summary>
+        public Exception? ProviderFailure { get; set; }
+
+        /// <summary>
+        /// Whether the attempt holds every stored vector the document still needs, so it stays when it fails, cf. CleanupFailedDocumentAsync.
+        /// </summary>
+        /// <remarks>
+        /// True once the attempt got through the whole document, even when the embedding provider
+        /// failed on the way: each chunk whose text the document had stored in any generation took
+        /// over that vector. True as well as soon as the provider fails for a document which had
+        /// nothing stored: no chunk after that could take over a vector, so the attempt stops there.
+        /// </remarks>
+        public bool HoldsEveryStoredVector { get; set; }
+    }
 
     public IIndexedDataSource DataSource => dataSource;
 
@@ -134,45 +169,81 @@ internal sealed class IndexedRunContext(IIndexedDataSource dataSource, Embedding
     public void PublishStatus(DataSourceEmbeddingStatus status) => publishStatus(status);
 
     /// <summary>
-    /// Embeds one document and stores it, in place of whatever was stored for it before.
+    /// Embeds one document and stores its chunks as a new generation, next to whatever it had stored before.
     /// </summary>
     /// <remarks>
-    /// The old vectors and the old index row go first, then the row is written anew with a chunk
-    /// count of zero, so the chunks have something to point at while they arrive batch by batch.
-    /// The final row, with the real chunk count, is written by whoever decides that the document
-    /// was indexed: only the kind of data source knows whether it changed in the meantime.
+    /// Which chunks the document has stored is read first. Each chunk whose text the document had
+    /// before takes over the stored vector instead of going to the embedding provider again. The
+    /// new chunks belong to the next generation and have ids of their own, so none of them
+    /// overwrites an old one.<br/><br/>
+    /// A document indexed before keeps its row, its chunks and its vectors meanwhile: the new
+    /// generation replaces them only once whoever indexes records the document as indexed, cf.
+    /// CompleteDocumentAsync, since only the kind of data source knows whether the document changed
+    /// in the meantime. Until then, no search finds the new generation, cf.
+    /// IndexStoreClient.GetHiddenChunksAsync. A document indexed for the first time gets a row with
+    /// a chunk count of zero, so its chunks have something to point at while they arrive.<br/><br/>
+    /// Once the embedding provider fails, it is asked nothing more for this document, and the rest
+    /// of the document is read only for the chunks which can take over a stored vector. So the
+    /// attempt ends up with every stored vector the document still needs, and stays next to the
+    /// stored version when it is cleaned up, cf. CleanupFailedDocumentAsync. The failure of the
+    /// provider is thrown at the end, as it was. A document which had nothing stored stops right
+    /// at the failure instead, since none of its chunks could take over a vector. Every other
+    /// failure is thrown right away.
     /// </remarks>
     /// <param name="document">The document to index.</param>
     /// <param name="reportBlockProgress">Told about every chunk, with its number and its page.</param>
     /// <param name="token">The cancellation token.</param>
-    /// <returns>The number of chunks stored for the document.</returns>
-    public async Task<int> IndexDocumentAsync(EmbeddingDocument document, Action<int, int?> reportBlockProgress, CancellationToken token)
+    /// <returns>What was stored for the document.</returns>
+    public async Task<IndexedDocument> IndexDocumentAsync(EmbeddingDocument document, Action<int, int?> reportBlockProgress, CancellationToken token)
     {
+        var reusableVectors = await ReusableVectors.ReadAsync(indexStore, dataSource.Id, document.Key, token);
+        var attempt = new IndexingAttempt(reusableVectors.NextGeneration, reusableVectors.StoredGenerations);
+        this.attempts[document.Key] = attempt;
+
         logger.LogDebug(
-            "Resetting stored embeddings for file '{FilePath}' in collection '{CollectionName}' before re-indexing.",
+            "Indexing file '{FilePath}' in collection '{CollectionName}' as generation {Generation}. What it had stored stays until the new chunks are complete.",
             document.Key,
-            this.CollectionName);
-        await this.DeleteDocumentPointsAsync(document.Key, token);
-        await indexStore.DeleteFileAsync(dataSource.Id, document.Key, token);
-        await indexStore.UpsertFileAsync(dataSource.Id, document.State, token);
+            this.CollectionName,
+            attempt.Generation);
+
+        //
+        // A document which was never indexed completely gets its row now, whose chunk count of zero
+        // hides it from every search. An attempt it kept before stays under the same row, so this one
+        // reuses its vectors, and a failure leaves them in place, cf. CleanupFailedDocumentAsync:
+        //
+        if (!manifest.Files.ContainsKey(document.Key))
+            await indexStore.UpsertFileAsync(dataSource.Id, document.State with { Generation = attempt.Generation }, token);
 
         var embeddingBatchSize = Math.Max(1, embeddingProvider.EffectiveEmbeddingBatchSize);
         var batch = new List<EmbeddingChunkDraft>(embeddingBatchSize);
         var totalChunkCount = 0;
-        var chunkIdSource = IndexedDocumentIds.CreateChunkIdSource(dataSource.Id, document.Key, document.State.ParentFileId, document.State.Fingerprint);
+        var storedChunkCount = 0;
+        var reusedChunkCount = 0;
+        var storedChunkIds = new List<string>();
+        var chunkIdSource = IndexedDocumentIds.CreateChunkIdSource(dataSource.Id, document.Key, document.State.ParentFileId, document.State.Fingerprint, attempt.Generation);
 
         await foreach (var chunk in document.StreamChunks(token))
         {
-            batch.Add(new(IndexedDocumentIds.CreateChunkId(dataSource.Id, chunkIdSource, totalChunkCount), chunk.Text, totalChunkCount, chunk.PageNumber));
+            var chunkId = IndexedDocumentIds.CreateChunkId(dataSource.Id, chunkIdSource, totalChunkCount);
+            batch.Add(new(chunkId, chunk, ChunkTextHash.Of(chunk.Text), totalChunkCount));
+            storedChunkIds.Add(chunkId);
             totalChunkCount++;
             reportBlockProgress(totalChunkCount, chunk.PageNumber);
 
             if (batch.Count >= embeddingBatchSize)
-                await this.FlushBatchAsync(document, batch, token);
+            {
+                var storedBatch = await this.FlushBatchAsync(document, batch, reusableVectors, attempt, token);
+                storedChunkCount += storedBatch.StoredCount;
+                reusedChunkCount += storedBatch.ReusedCount;
+            }
         }
 
         if (batch.Count > 0)
-            await this.FlushBatchAsync(document, batch, token);
+        {
+            var storedBatch = await this.FlushBatchAsync(document, batch, reusableVectors, attempt, token);
+            storedChunkCount += storedBatch.StoredCount;
+            reusedChunkCount += storedBatch.ReusedCount;
+        }
 
         //
         // The extraction itself did not report a failure, but nothing usable came out of it. For
@@ -182,6 +253,20 @@ internal sealed class IndexedRunContext(IIndexedDataSource dataSource, Embedding
         if (totalChunkCount == 0)
             throw new FileExtractionException(FileExtractionErrorCode.NO_CONTENT, string.Format(TB("No text could be read from '{0}'."), document.Key));
 
+        attempt.HoldsEveryStoredVector = true;
+        if (attempt.ProviderFailure is not null)
+        {
+            logger.LogInformation(
+                "Read file '{FilePath}' in data source '{DataSourceName}' ({DataSourceId}) to its end without asking the failed embedding provider again. {StoredChunkCount} of {ChunkCount} chunks were stored with a vector, and stay for the next attempt.",
+                document.Key,
+                dataSource.Name,
+                dataSource.Id,
+                storedChunkCount,
+                totalChunkCount);
+
+            ExceptionDispatchInfo.Throw(attempt.ProviderFailure);
+        }
+
         logger.LogDebug(
             "Generated {ChunkCount} chunks for file '{FilePath}' in data source '{DataSourceName}' ({DataSourceId}).",
             totalChunkCount,
@@ -189,7 +274,128 @@ internal sealed class IndexedRunContext(IIndexedDataSource dataSource, Embedding
             dataSource.Name,
             dataSource.Id);
 
-        return totalChunkCount;
+        if (reusedChunkCount > 0)
+            logger.LogInformation(
+                "Reused the stored vectors of {ReusedChunkCount} of {ChunkCount} chunks for file '{FilePath}' in data source '{DataSourceName}' ({DataSourceId}). Only the other chunks went to the embedding provider.",
+                reusedChunkCount,
+                totalChunkCount,
+                document.Key,
+                dataSource.Name,
+                dataSource.Id);
+
+        return new(totalChunkCount, attempt.Generation, storedChunkIds);
+    }
+
+    /// <summary>
+    /// Completes a document indexed again: its new generation stays, and every other one goes, in both stores.
+    /// </summary>
+    /// <remarks>
+    /// Called by whoever records the document as indexed, cf. DocumentRunProgress.RecordDocumentIndexedAsync,
+    /// right after its row names the new generation. From then on, no search finds the other
+    /// generations, cf. IndexStoreClient.GetHiddenChunksAsync, so a store which refuses to remove
+    /// them costs space, not the document. The next indexing of the document removes them then.
+    /// Whatever an interrupted run left behind for the document goes as well, since it belongs to
+    /// no generation the document keeps.
+    /// </remarks>
+    /// <param name="documentKey">The key of the document.</param>
+    /// <param name="indexed">What indexing the document stored.</param>
+    /// <param name="token">The cancellation token.</param>
+    public async Task CompleteDocumentAsync(string documentKey, IndexedDocument indexed, CancellationToken token)
+    {
+        this.attempts.Remove(documentKey);
+        try
+        {
+            await this.KeepGenerationsAsync(documentKey, [indexed.Generation], indexed.ChunkIds, token);
+        }
+        catch (OperationCanceledException) when (token.IsCancellationRequested)
+        {
+            throw;
+        }
+        catch (Exception exception)
+        {
+            logger.LogWarning(
+                exception,
+                "Could not remove the earlier generations of file '{FilePath}' in data source '{DataSourceName}' ({DataSourceId}) after it was indexed. No search finds them, and the next indexing of the file removes them.",
+                documentKey,
+                dataSource.Name,
+                dataSource.Id);
+        }
+    }
+
+    /// <summary>
+    /// Removes what failed attempts and interrupted runs left behind of documents which are complete and did not change since.
+    /// </summary>
+    /// <remarks>
+    /// The next indexing of a document removes such generations, cf. CompleteDocumentAsync. A
+    /// document which did not change since is not indexed again, though, e.g., a file whose edit was
+    /// undone, or one whose run stopped while removing them, so nothing else would ever remove
+    /// them. No search finds them, so they cost space only, and a failure here costs the run nothing.
+    /// </remarks>
+    /// <param name="isUnchanged">Whether the document with the given key is the same as what its row describes.</param>
+    /// <param name="token">The cancellation token.</param>
+    public async Task RemoveLeftoverGenerationsAsync(Func<string, bool> isUnchanged, CancellationToken token)
+    {
+        try
+        {
+            // The documents with hidden chunks, which are few. A document whose first indexing is not complete has none to search by, and stays as it is:
+            var documents = await indexStore.GetHiddenChunksAsync(dataSource.Id, token);
+            if (documents.Count is 0)
+                return;
+
+            var keysByParentId = new Dictionary<string, string>(StringComparer.Ordinal);
+            foreach (var (key, record) in manifest.Files)
+                if (record.ParentFileId is { } parentFileId)
+                    keysByParentId.TryAdd(parentFileId, key);
+
+            foreach (var document in documents)
+            {
+                token.ThrowIfCancellationRequested();
+                if (document.SearchableGeneration is { } generation && keysByParentId.TryGetValue(document.ParentFileId, out var key) && manifest.Files[key].Generation == generation && isUnchanged(key))
+                    await this.KeepOnlyGenerationAsync(key, generation, token);
+            }
+        }
+        catch (OperationCanceledException) when (token.IsCancellationRequested)
+        {
+            throw;
+        }
+        catch (Exception exception)
+        {
+            logger.LogWarning(exception, "Could not remove what earlier runs left behind of the documents in data source '{DataSourceName}' ({DataSourceId}). No search finds it, and the next run tries again.", dataSource.Name, dataSource.Id);
+        }
+    }
+
+    /// <summary>
+    /// Removes every generation of a document but the given one, when it has any other.
+    /// </summary>
+    /// <param name="documentKey">The key of the document.</param>
+    /// <param name="generation">The generation which stays, the one its row names.</param>
+    /// <param name="token">The cancellation token.</param>
+    public async Task KeepOnlyGenerationAsync(string documentKey, int generation, CancellationToken token)
+    {
+        var storedChunks = await indexStore.GetStoredChunksAsync(dataSource.Id, documentKey, token);
+        if (storedChunks.All(chunk => chunk.Generation == generation))
+            return;
+
+        await this.KeepGenerationsAsync(documentKey, [generation], storedChunks.Where(chunk => chunk.Generation == generation).Select(chunk => chunk.ChunkId).ToList(), token);
+    }
+
+    /// <summary>
+    /// Removes every generation of a document but the given ones, from the vector store first.
+    /// </summary>
+    /// <remarks>
+    /// The index store forgets a chunk only once its point is gone. As long as it knows a chunk, no
+    /// search finds the chunk unless it belongs to the generation the document is searched by, cf.
+    /// IndexStoreClient.GetHiddenChunksAsync. A point the index store no longer knew of could be
+    /// found by the vector search.
+    /// </remarks>
+    /// <param name="documentKey">The key of the document.</param>
+    /// <param name="generations">The generations which stay.</param>
+    /// <param name="chunkIds">The ids of their chunks, which are the points that stay.</param>
+    /// <param name="token">The cancellation token.</param>
+    private async Task KeepGenerationsAsync(string documentKey, IReadOnlyCollection<int> generations, IReadOnlyCollection<string> chunkIds, CancellationToken token)
+    {
+        await this.DeleteDocumentPointsAsync(documentKey, chunkIds, token);
+        await indexStore.DeleteOtherGenerationsAsync(dataSource.Id, documentKey, generations, token);
     }
 
     /// <summary>
@@ -197,19 +403,40 @@ internal sealed class IndexedRunContext(IIndexedDataSource dataSource, Embedding
     /// </summary>
     /// <param name="documentKey">The key of the document.</param>
     /// <param name="token">The cancellation token.</param>
-    public async Task DeleteDocumentPointsAsync(string documentKey, CancellationToken token)
+    public Task DeleteDocumentPointsAsync(string documentKey, CancellationToken token) => this.DeleteDocumentPointsAsync(documentKey, [], token);
+
+    /// <summary>
+    /// Removes the vectors of one document from the collection, apart from the given ones.
+    /// </summary>
+    /// <param name="documentKey">The key of the document.</param>
+    /// <param name="keepPointIds">The points of the document which stay.</param>
+    /// <param name="token">The cancellation token.</param>
+    private async Task DeleteDocumentPointsAsync(string documentKey, IReadOnlyCollection<string> keepPointIds, CancellationToken token)
     {
         // A relocated document keeps its original parent id. Delete by that identity as well as
         // by path, including when a previous relocation stopped between its two database writes.
         var parentId = manifest.Files.GetValueOrDefault(documentKey)?.ParentFileId ?? string.Empty;
-        await vectorStore.DeleteEmbeddingByFile(this.CollectionName, documentKey, parentId, token);
+        await vectorStore.DeleteEmbeddingByFile(this.CollectionName, documentKey, parentId, keepPointIds, token);
         this.hasPendingChanges = true;
     }
 
     /// <summary>
-    /// Removes whatever a failed attempt left behind of one document.
+    /// Sorts out what a failed attempt left behind of one document.
     /// </summary>
     /// <remarks>
+    /// A document indexed before keeps the version it had. That holds for every failure, one which
+    /// lies in the document included: a file broken by an edit may be fixed again, and meanwhile
+    /// its last good version can still be found.<br/><br/>
+    /// An attempt which holds every stored vector the document still needs stays as well, though
+    /// no search finds it, cf. IndexStoreClient.GetHiddenChunksAsync: one which got through the
+    /// whole document, or one of a document which had nothing stored when the embedding provider
+    /// failed. The vectors it got from the provider before the failure are among them, so the next
+    /// attempt asks the provider only for the rest. Every other generation goes, so a document
+    /// keeps two at most. Any other attempt goes instead, and what the document had stored before
+    /// it stays as it was.<br/><br/>
+    /// A document indexed for the first time has no version to keep. It keeps an attempt which
+    /// holds its vectors, under a row whose chunk count stays zero. Otherwise, it keeps what an
+    /// earlier attempt kept, and loses everything when there is none.<br/><br/>
     /// Never throws for a store which refuses: the document already failed, and that failure is the
     /// one the user has to hear about.
     /// </remarks>
@@ -217,27 +444,34 @@ internal sealed class IndexedRunContext(IIndexedDataSource dataSource, Embedding
     /// <param name="token">The cancellation token.</param>
     public async Task CleanupFailedDocumentAsync(string documentKey, CancellationToken token)
     {
-        try
+        var storedVersion = manifest.Files.GetValueOrDefault(documentKey);
+        this.attempts.Remove(documentKey, out var attempt);
+
+        // The attempt failed before it wrote anything, so what the document had stays as it was:
+        if (attempt is null)
+            return;
+
+        IReadOnlyCollection<int> keptGenerations = (storedVersion, attempt) switch
         {
-            await this.DeleteDocumentPointsAsync(documentKey, token);
-        }
-        catch (OperationCanceledException) when (token.IsCancellationRequested)
-        {
-            throw;
-        }
-        catch (Exception exception)
-        {
-            logger.LogWarning(
-                exception,
-                "Could not remove vector points while cleaning up failed embedding for file '{FilePath}' in data source '{DataSourceName}' ({DataSourceId}).",
-                documentKey,
-                dataSource.Name,
-                dataSource.Id);
-        }
+            (null, { HoldsEveryStoredVector: true } kept) => [kept.Generation],
+            ({ } stored, { HoldsEveryStoredVector: true } kept) => [stored.Generation, kept.Generation],
+            _ => attempt.EarlierGenerations,
+        };
 
         try
         {
-            await indexStore.DeleteFileAsync(dataSource.Id, documentKey, token);
+            IReadOnlyList<string> keptChunkIds = keptGenerations.Count is 0 ? [] : await indexStore.GetChunkIdsAsync(dataSource.Id, documentKey, keptGenerations, token);
+            if (storedVersion is null && keptChunkIds.Count is 0)
+            {
+                await this.DeleteDocumentPointsAsync(documentKey, token);
+                await indexStore.DeleteFileAsync(dataSource.Id, documentKey, token);
+                manifest.UnfinishedFiles.Remove(documentKey);
+                return;
+            }
+
+            await this.KeepGenerationsAsync(documentKey, keptGenerations, keptChunkIds, token);
+            if (storedVersion is null)
+                manifest.UnfinishedFiles.Add(documentKey);
         }
         catch (OperationCanceledException) when (token.IsCancellationRequested)
         {
@@ -247,7 +481,7 @@ internal sealed class IndexedRunContext(IIndexedDataSource dataSource, Embedding
         {
             logger.LogWarning(
                 exception,
-                "Could not remove embedding state while cleaning up failed embedding for file '{FilePath}' in data source '{DataSourceName}' ({DataSourceId}).",
+                "Could not remove what a failed attempt left behind of file '{FilePath}' in data source '{DataSourceName}' ({DataSourceId}). No search finds it, and the next attempt removes it.",
                 documentKey,
                 dataSource.Name,
                 dataSource.Id);
@@ -318,16 +552,168 @@ internal sealed class IndexedRunContext(IIndexedDataSource dataSource, Embedding
         this.hasPendingChanges = false;
     }
 
-    private async Task FlushBatchAsync(EmbeddingDocument document, List<EmbeddingChunkDraft> batch, CancellationToken token)
+    /// <summary>
+    /// Stores one batch of chunks, each with its vector, and leaves out the chunks without one.
+    /// </summary>
+    /// <remarks>
+    /// A chunk goes without a vector only once the embedding provider failed for the document, cf.
+    /// IndexDocumentAsync.
+    /// </remarks>
+    /// <param name="document">The document the chunks belong to.</param>
+    /// <param name="batch">The chunks, emptied once they are stored.</param>
+    /// <param name="reusableVectors">The chunks the document had stored before.</param>
+    /// <param name="attempt">The attempt the chunks belong to, which remembers whether the embedding provider failed.</param>
+    /// <param name="token">The cancellation token.</param>
+    /// <returns>How many of the chunks were stored, and how many of those kept a stored vector instead of being embedded.</returns>
+    private async Task<StoredBatch> FlushBatchAsync(EmbeddingDocument document, List<EmbeddingChunkDraft> batch, ReusableVectors reusableVectors, IndexingAttempt attempt, CancellationToken token)
+    {
+        //
+        // A chunk whose text the document had stored before takes that vector over. Only the other
+        // chunks go to the embedding provider:
+        //
+        var storedVectors = await reusableVectors.TakeAsync(vectorStore, this.CollectionName, manifest.VectorSize, batch.Select(chunk => chunk.TextHash).ToList(), token);
+        var vectors = new IReadOnlyList<float>?[batch.Count];
+        var chunksToEmbed = new List<int>(batch.Count);
+        for (var index = 0; index < batch.Count; index++)
+        {
+            if (storedVectors[index] is { } storedVector)
+                vectors[index] = storedVector;
+            else
+                chunksToEmbed.Add(index);
+        }
+
+        var reusedChunkCount = batch.Count - chunksToEmbed.Count;
+        if (chunksToEmbed.Count > 0 && attempt.ProviderFailure is null)
+        {
+            IReadOnlyList<IReadOnlyList<float>>? embeddedVectors = null;
+            try
+            {
+                embeddedVectors = await this.RequestVectorsAsync(document, chunksToEmbed.Select(index => batch[index].Text).ToList(), token);
+            }
+            catch (Exception exception) when (exception is not OperationCanceledException || !token.IsCancellationRequested)
+            {
+                //
+                // A document which had nothing stored has no chunk which could take over a vector,
+                // so reading on would only cost time. What the attempt embedded so far stays:
+                //
+                if (attempt.EarlierGenerations.Count is 0)
+                {
+                    attempt.HoldsEveryStoredVector = true;
+                    throw;
+                }
+
+                //
+                // The provider is asked nothing more for this document. It may be down, and once
+                // the cause is fixed, e.g., a chunk too long for it, the chunks after that one may
+                // be cut differently, so whatever it embedded meanwhile would be paid for nothing.
+                // The rest of the document is still read, for the chunks with a stored vector:
+                //
+                attempt.ProviderFailure = exception;
+                logger.LogDebug(
+                    "The embedding provider failed for file '{FilePath}' in data source '{DataSourceName}' ({DataSourceId}). The rest of the file is read for the chunks with a stored vector only.",
+                    document.Key,
+                    dataSource.Name,
+                    dataSource.Id);
+            }
+
+            if (embeddedVectors is not null)
+            {
+                await this.EnsureCollectionAsync(embeddedVectors[0].Count, token);
+                for (var position = 0; position < chunksToEmbed.Count; position++)
+                    vectors[chunksToEmbed[position]] = embeddedVectors[position];
+            }
+        }
+
+        var chunksToStore = Enumerable.Range(0, batch.Count).Where(index => vectors[index] is not null).ToList();
+        if (chunksToStore.Count > 0)
+        {
+            token.ThrowIfCancellationRequested();
+            var embeddedAtUtc = DateTimeOffset.UtcNow;
+            var state = document.State;
+            var points = chunksToStore.Select(index => new VectorStoragePoint(
+                batch[index].ChunkId,
+                vectors[index]!,
+                dataSource.Id,
+                dataSource.Type.ToString(),
+                batch[index].ChunkId,
+                state.ParentFileId,
+                document.Key,
+                state.AbsolutePath,
+                state.FileName,
+                state.RelativePath,
+                state.FileType,
+                batch[index].Chunk.PageNumber,
+                batch[index].Chunk.EndPageNumber,
+                batch[index].ChunkIndex,
+                batch[index].Text,
+                state.Fingerprint,
+                state.CreationUtc,
+                state.LastWriteUtc,
+                embeddedAtUtc,
+                attempt.Generation)).ToList();
+
+            //
+            // The vector store keeps the pages only, cf. VectorStoragePoint. Everything else about
+            // where a chunk is goes into the index store alone:
+            //
+            var chunks = chunksToStore
+                .Select(index => batch[index])
+                .Select(draft => new EmbeddingStateChunk(
+                    draft.ChunkId,
+                    state.ParentFileId,
+                    draft.Chunk.PageNumber,
+                    draft.Chunk.EndPageNumber,
+                    draft.ChunkIndex,
+                    draft.Text,
+                    embeddedAtUtc,
+                    draft.TextHash,
+                    attempt.Generation,
+                    draft.Chunk.Start.SheetName,
+                    draft.Chunk.Start.RowNumber,
+                    draft.Chunk.End.RowNumber,
+                    draft.Chunk.Start.LineNumber,
+                    draft.Chunk.End.LineNumber,
+                    draft.Chunk.AttachmentPosition))
+                .ToList();
+
+            //
+            // The index store first: as long as it knows the chunks of the new generation, no search
+            // finds them, cf. IndexStoreClient.GetHiddenChunksAsync. A point it did not know yet, e.g.,
+            // after the app stopped right here, would be found next to the stored version:
+            //
+            await indexStore.UpsertChunksAsync(dataSource.Id, chunks, token);
+            token.ThrowIfCancellationRequested();
+
+            await vectorStore.InsertEmbedding(this.CollectionName, points, token);
+            await this.RecordStoredChunksAsync(chunksToStore.Count, token);
+
+            logger.LogDebug(
+                "Stored {ChunkCount} embedded chunks for file '{FilePath}' in collection '{CollectionName}'.",
+                chunksToStore.Count,
+                document.Key,
+                this.CollectionName);
+        }
+
+        batch.Clear();
+        return new(chunksToStore.Count, reusedChunkCount);
+    }
+
+    /// <summary>
+    /// Asks the embedding provider for the vectors of some texts, and checks them before anything is stored.
+    /// </summary>
+    /// <param name="document">The document the texts belong to.</param>
+    /// <param name="texts">The texts.</param>
+    /// <param name="token">The cancellation token.</param>
+    /// <returns>One vector per text, in the same order.</returns>
+    private async Task<IReadOnlyList<IReadOnlyList<float>>> RequestVectorsAsync(EmbeddingDocument document, List<string> texts, CancellationToken token)
     {
         logger.LogDebug(
             "Requesting embeddings for batch of {ChunkCount} chunks from file '{FilePath}' in data source '{DataSourceName}' ({DataSourceId}).",
-            batch.Count,
+            texts.Count,
             document.Key,
             dataSource.Name,
             dataSource.Id);
 
-        var texts = batch.Select(item => item.Text).ToList();
         IReadOnlyList<IReadOnlyList<float>> vectors;
         try
         {
@@ -353,11 +739,11 @@ internal sealed class IndexedRunContext(IIndexedDataSource dataSource, Embedding
             // The messages of these exceptions end up in the log, never in front of the user, so
             // they name the document by its key: the name a user reads may be the subject of a mail.
             //
-            throw new InvalidOperationException(string.Format(TB("The embedding provider was not able to embed {0} part(s) of '{1}'. The provider reported: {2}"), batch.Count, document.Key, exception.Message), exception);
+            throw new InvalidOperationException(string.Format(TB("The embedding provider was not able to embed {0} part(s) of '{1}'. The provider reported: {2}"), texts.Count, document.Key, exception.Message), exception);
         }
 
-        if (vectors.Count != batch.Count)
-            throw new InvalidOperationException(string.Format(TB("The embedding provider answered with {0} vectors for {1} parts of '{2}'. Please select another embedding model or provider."), vectors.Count, batch.Count, document.Key));
+        if (vectors.Count != texts.Count)
+            throw new InvalidOperationException(string.Format(TB("The embedding provider answered with {0} vectors for {1} parts of '{2}'. Please select another embedding model or provider."), vectors.Count, texts.Count, document.Key));
 
         var vectorSize = vectors.FirstOrDefault()?.Count ?? 0;
         if (vectorSize <= 0)
@@ -372,6 +758,16 @@ internal sealed class IndexedRunContext(IIndexedDataSource dataSource, Embedding
         if (manifest.VectorSize > 0 && manifest.VectorSize != vectorSize)
             throw new InvalidOperationException(string.Format(TB("The size of the embedding vectors changed from {0} to {1}. Please save the data source again to index it from scratch."), manifest.VectorSize, vectorSize));
 
+        return vectors;
+    }
+
+    /// <summary>
+    /// Creates the store of the data source with the first vectors it gets, which decide its size.
+    /// </summary>
+    /// <param name="vectorSize">The size of the vectors the embedding provider answered with.</param>
+    /// <param name="token">The cancellation token.</param>
+    private async Task EnsureCollectionAsync(int vectorSize, CancellationToken token)
+    {
         if (manifest.VectorSize == 0)
         {
             token.ThrowIfCancellationRequested();
@@ -398,46 +794,5 @@ internal sealed class IndexedRunContext(IIndexedDataSource dataSource, Embedding
                 dataSource.Name,
                 dataSource.Id);
         }
-
-        token.ThrowIfCancellationRequested();
-        var embeddedAtUtc = DateTimeOffset.UtcNow;
-        var state = document.State;
-        var points = batch.Select((item, index) => new VectorStoragePoint(
-            item.ChunkId,
-            vectors[index],
-            dataSource.Id,
-            dataSource.Type.ToString(),
-            item.ChunkId,
-            state.ParentFileId,
-            document.Key,
-            state.AbsolutePath,
-            state.FileName,
-            state.RelativePath,
-            state.FileType,
-            item.PageNumber,
-            item.ChunkIndex,
-            item.Text,
-            state.Fingerprint,
-            state.CreationUtc,
-            state.LastWriteUtc,
-            embeddedAtUtc)).ToList();
-
-        await vectorStore.InsertEmbedding(this.CollectionName, points, token);
-        token.ThrowIfCancellationRequested();
-
-        var chunks = batch
-            .Select(chunk => new EmbeddingStateChunk(chunk.ChunkId, state.ParentFileId, chunk.PageNumber, chunk.ChunkIndex, chunk.Text, embeddedAtUtc))
-            .ToList();
-
-        await indexStore.UpsertChunksAsync(dataSource.Id, chunks, token);
-        await this.RecordStoredChunksAsync(batch.Count, token);
-
-        logger.LogDebug(
-            "Stored {ChunkCount} embedded chunks for file '{FilePath}' in collection '{CollectionName}'.",
-            batch.Count,
-            document.Key,
-            this.CollectionName);
-
-        batch.Clear();
     }
 }

app/MindWork AI Studio/Tools/Services/Indexing/MailboxIndexer.Attachments.cs

@@ -73,29 +73,36 @@ internal sealed partial class MailboxIndexer
     /// </summary>
     /// <remarks>
     /// Each attachment is cut on its own, by the strategy of its file type, and its first chunk
-    /// names it. A chunk of an attachment carries no page: the chunks of a mail are told apart by
-    /// the mail alone, so a page would not say which attachment it is a page of.
+    /// names it. A chunk of an attachment knows which one it is from, by the position of that
+    /// attachment among all attachments of the mail, the way the index numbers them in mail_parts,
+    /// so its pages, rows or lines say where in that attachment it is.
     /// </remarks>
+    /// <param name="textChunker">Cuts the text of the mail and of its attachments into chunks.</param>
     /// <param name="mailContent">The header block and the text of the mail.</param>
     /// <param name="attachments">The attachments, those whose text was not read included.</param>
     /// <param name="options">How large a chunk may become.</param>
     /// <param name="embeddingProvider">The embedding provider whose tokenizer measures the chunks.</param>
     /// <param name="token">The cancellation token.</param>
     /// <returns>The chunks of the mail, in order.</returns>
-    private async IAsyncEnumerable<EmbeddingChunk> StreamMailChunksAsync(SegmentedText mailContent, IReadOnlyList<MailAttachmentText> attachments, ChunkingOptions options, EmbeddingProvider embeddingProvider, [EnumeratorCancellation] CancellationToken token)
+    internal static async IAsyncEnumerable<EmbeddingChunk> StreamMailChunksAsync(TextChunker textChunker, SegmentedText mailContent, IReadOnlyList<MailAttachmentText> attachments, ChunkingOptions options, EmbeddingProvider embeddingProvider, [EnumeratorCancellation] CancellationToken token)
     {
         await foreach (var chunk in textChunker.SplitAsync(mailContent, TextChunker.DOCUMENT_STRATEGY, options, embeddingProvider, token))
             yield return chunk;
 
-        foreach (var attachment in attachments)
+        //
+        // Counted over every attachment, those without text included, since the index numbers
+        // them that way, cf. CreateMailRecord:
+        //
+        for (var position = 0; position < attachments.Count; position++)
         {
+            var attachment = attachments[position];
             if (attachment.TextState is not MailPartTextState.EXTRACTED || attachment.Content.Text.Length is 0)
                 continue;
 
             // In English like the header block, cf. MailTextBuilder:
             var heading = attachment.Name.Length > 0 ? $"Attachment: {attachment.Name}" : "Attachment without a name";
             await foreach (var chunk in textChunker.SplitAsync(attachment.Content, attachment.Strategy, options, embeddingProvider, token, heading))
-                yield return chunk with { PageNumber = null };
+                yield return chunk with { AttachmentPosition = position };
         }
     }
 }

app/MindWork AI Studio/Tools/Services/Indexing/MailboxIndexer.Mails.cs

@@ -98,10 +98,14 @@ internal sealed partial class MailboxIndexer
             document = this.CreateMailDocument(context, mailbox, summary, key, mailId, mailHash, displayName, foundAtUtc, text, attachments);
 
             var reportBlockProgress = progress.BeginDocument(document);
-            var chunkCount = await context.IndexDocumentAsync(document, reportBlockProgress, token);
-            await progress.RecordDocumentIndexedAsync(document, chunkCount, isNew, token);
+            var indexed = await context.IndexDocumentAsync(document, reportBlockProgress, token);
+            await progress.RecordDocumentIndexedAsync(document, indexed, isNew, token);
 
-            // Only after the last chunk: indexing the document deleted whatever the index kept of the mail.
+            //
+            // Only after the last chunk: a mail indexed for the first time gets its row with its
+            // first chunk, and the rows of the mail point at it. One indexed before keeps its rows,
+            // which are written anew here.
+            //
             await context.IndexStore.UpsertMailAsync(mailbox.Id, CreateMailRecord(mailId, summary, text, attachments, mailHash, location, foundAtUtc), token);
         }
         catch (OperationCanceledException) when (token.IsCancellationRequested)
@@ -196,10 +200,10 @@ internal sealed partial class MailboxIndexer
         // search for a sender or a subject finds the mail. The attachments follow it.
         //
         var fullText = text?.FullText ?? string.Empty;
-        var content = new SegmentedText(fullText, fullText.Length is 0 ? [] : [new TextSegment(fullText, null, null)]);
+        var content = new SegmentedText(fullText, fullText.Length is 0 ? [] : [new TextSegment(fullText, null, default)]);
         var chunkingOptions = DataSourceEmbeddingService.GetChunkingOptions(mailbox, context.EmbeddingProvider);
 
-        return new(key, state, displayName, chunkToken => this.StreamMailChunksAsync(content, attachments, chunkingOptions, context.EmbeddingProvider, chunkToken));
+        return new(key, state, displayName, chunkToken => StreamMailChunksAsync(textChunker, content, attachments, chunkingOptions, context.EmbeddingProvider, chunkToken));
     }
 
     /// <summary>

app/MindWork AI Studio/Tools/Services/Indexing/MailboxIndexer.cs

@@ -275,6 +275,7 @@ internal sealed partial class MailboxIndexer(SettingsManager settingsManager, Ru
 
             var deletedMails = await this.ApplyRemovalsAsync(context, mailbox, plannedFolders, removals, runStartedUtc, token);
             await ForgetVanishedFailuresAsync(context, encounteredKeys, token);
+            await ForgetVanishedAttemptsAsync(context, encounteredKeys, token);
 
             var completedUtc = DateTimeOffset.UtcNow;
             await context.IndexStore.CompleteMailboxSyncAsync(mailbox.Id, completedUtc, token);
@@ -529,6 +530,27 @@ internal sealed partial class MailboxIndexer(SettingsManager settingsManager, Ru
             await context.ForgetPermanentFailureAsync(key, token);
     }
 
+    /// <summary>
+    /// Removes what failed attempts kept of mails which did not turn up during this run.
+    /// </summary>
+    /// <remarks>
+    /// An attempt which failed at the embedding provider keeps its vectors for the next one, under a
+    /// row without chunks, cf. IndexedRunContext.CleanupFailedDocumentAsync. Such a mail has no
+    /// location yet, so every run comes across it among the new mails, for as long as it belongs
+    /// into the index. One which did not turn up is gone, and what its attempt kept would stay
+    /// forever, hidden from every search, but asked about before each one.
+    /// </remarks>
+    private static async Task ForgetVanishedAttemptsAsync(IndexedRunContext context, IReadOnlySet<string> encounteredKeys, CancellationToken token)
+    {
+        foreach (var key in context.Manifest.UnfinishedFiles.Where(key => !encounteredKeys.Contains(key)).ToList())
+        {
+            token.ThrowIfCancellationRequested();
+            await context.DeleteDocumentPointsAsync(key, token);
+            await context.IndexStore.DeleteFileAsync(context.DataSource.Id, key, token);
+            context.Manifest.UnfinishedFiles.Remove(key);
+        }
+    }
+
     /// <summary>
     /// Tells the user interface how the mailbox stands, from the index alone.
     /// </summary>

app/MindWork AI Studio/Tools/Services/Indexing/ReusableVectors.cs

@@ -0,0 +1,94 @@
+using AIStudio.Tools.Databases.IndexStore;
+using AIStudio.Tools.Databases.VectorStore;
+
+namespace AIStudio.Tools.Services.Indexing;
+
+/// <summary>
+/// The chunks a document had stored before it is read again, so that a chunk whose text did not
+/// change keeps its vector.
+/// </summary>
+/// <remarks>
+/// A vector depends on nothing but its text and the embedding signature, and all vectors of one
+/// store share that signature: another one drops the store. So a chunk whose text is byte for byte
+/// the text of a chunk the document had stored may take over that vector, instead of going to the
+/// embedding provider again. That spares a file which was only saved again, or changed near its
+/// end, almost every request.<br/><br/>
+/// Only the id and the hash of each stored chunk are held in memory, about a hundred bytes per
+/// chunk. The vectors stay in the vector store until the run is done with the document, and each
+/// batch reads the few it can use, cf. TakeAsync. The new chunks belong to the next generation and
+/// so have ids of their own, cf. NextGeneration: writing them never overwrites a vector a later
+/// chunk may still need.
+/// </remarks>
+internal sealed class ReusableVectors
+{
+    private readonly Dictionary<string, string> chunkIdsByTextHash = new(StringComparer.Ordinal);
+
+    private ReusableVectors(IReadOnlyList<StoredChunk> storedChunks)
+    {
+        foreach (var storedChunk in storedChunks)
+            this.chunkIdsByTextHash.TryAdd(storedChunk.TextHash, storedChunk.ChunkId);
+
+        //
+        // A document stored for the first time, or again after a failure removed all of it,
+        // starts at generation 0, which gives the ids documents got before generations existed:
+        //
+        this.NextGeneration = storedChunks.Count is 0 ? 0 : storedChunks.Max(storedChunk => storedChunk.Generation) + 1;
+        this.StoredGenerations = storedChunks.Select(storedChunk => storedChunk.Generation).ToHashSet();
+    }
+
+    /// <summary>
+    /// The generation of the chunks about to be written, cf. IndexedDocumentIds.CreateChunkIdSource.
+    /// </summary>
+    public int NextGeneration { get; }
+
+    /// <summary>
+    /// The generations the document has stored chunks of.
+    /// </summary>
+    public IReadOnlyCollection<int> StoredGenerations { get; }
+
+    /// <summary>
+    /// Reads which chunks a document has stored now, before anything of it is deleted.
+    /// </summary>
+    /// <param name="indexStore">The index store, which knows the chunks of the document and their texts.</param>
+    /// <param name="dataSourceId">The data source the document belongs to.</param>
+    /// <param name="documentKey">The key of the document.</param>
+    /// <param name="token">The cancellation token.</param>
+    /// <returns>The chunks of the document, which may be none.</returns>
+    public static async Task<ReusableVectors> ReadAsync(IndexStoreClient indexStore, string dataSourceId, string documentKey, CancellationToken token) =>
+        new(await indexStore.GetStoredChunksAsync(dataSourceId, documentKey, token));
+
+    /// <summary>
+    /// Finds the stored vector of every chunk of a batch whose text the document had before.
+    /// </summary>
+    /// <param name="vectorStore">The vector store, which still holds the vectors of the stored chunks.</param>
+    /// <param name="collectionName">The vector store of the data source.</param>
+    /// <param name="vectorSize">The size of the vectors in the store.</param>
+    /// <param name="textHashes">The text hash of each chunk of the batch.</param>
+    /// <param name="token">The cancellation token.</param>
+    /// <returns>For each chunk, in the same order, its stored vector, or null when it has to be embedded.</returns>
+    public async Task<IReadOnlyList<float>?[]> TakeAsync(VectorStoreClient vectorStore, string collectionName, int vectorSize, IReadOnlyList<string> textHashes, CancellationToken token)
+    {
+        var vectors = new IReadOnlyList<float>?[textHashes.Count];
+        if (this.chunkIdsByTextHash.Count == 0 || vectorSize <= 0)
+            return vectors;
+
+        var sourcePointIds = textHashes.Select(textHash => this.chunkIdsByTextHash.GetValueOrDefault(textHash)).ToArray();
+        var pointIdsToRead = sourcePointIds.OfType<string>().Distinct(StringComparer.OrdinalIgnoreCase).ToList();
+        if (pointIdsToRead.Count == 0)
+            return vectors;
+
+        //
+        // A vector of another size cannot come from this store as it is now, and the store would
+        // refuse it next to the others:
+        //
+        var storedVectors = (await vectorStore.RetrieveVectorsAsync(collectionName, pointIdsToRead, token))
+            .Where(storedVector => storedVector.Vector.Count == vectorSize)
+            .ToDictionary(storedVector => storedVector.PointId, storedVector => storedVector.Vector, StringComparer.OrdinalIgnoreCase);
+
+        for (var index = 0; index < textHashes.Count; index++)
+            if (sourcePointIds[index] is { } pointId && storedVectors.TryGetValue(pointId, out var storedVector))
+                vectors[index] = storedVector;
+
+        return vectors;
+    }
+}

app/MindWork AI Studio/Tools/Services/Indexing/StoredBatch.cs

@@ -0,0 +1,8 @@
+namespace AIStudio.Tools.Services.Indexing;
+
+/// <summary>
+/// How many chunks of a batch were stored, cf. IndexedRunContext.FlushBatchAsync.
+/// </summary>
+/// <param name="StoredCount">How many of the chunks were stored.</param>
+/// <param name="ReusedCount">How many of those kept a stored vector instead of being embedded.</param>
+internal readonly record struct StoredBatch(int StoredCount, int ReusedCount);

app/MindWork AI Studio/Tools/Services/Indexing/TextChunker.cs

@@ -114,15 +114,68 @@ internal sealed partial class TextChunker(RustService rustService, ILogger logge
     /// <returns>The chunks, in the order of the text.</returns>
     public async IAsyncEnumerable<EmbeddingChunk> SplitAsync(SegmentedText content, ChunkingStrategy strategy, ChunkingOptions options, EmbeddingProvider embeddingProvider, [System.Runtime.CompilerServices.EnumeratorCancellation] CancellationToken token, string heading = "")
     {
-        var estimatedTokenCount = SumTokenCounts(content.SourceSegments);
+        var requiredPrefix = heading;
+        foreach (var part in SplitBySheets(content))
+        {
+            var estimatedTokenCount = SumTokenCounts(part.SourceSegments);
 
-        // The whole text starts where the first segment starts, so that is the page it is on until
-        // the splitting reaches a segment boundary:
-        var firstPageNumber = content.SourceSegments.Count > 0 ? content.SourceSegments[0].PageNumber : null;
-        await foreach (var chunk in this.SplitTextByRulesAsync(content.Text, content.SourceSegments, strategy, 0, options, embeddingProvider, firstPageNumber, token, heading, estimatedTokenCount))
-            yield return chunk;
+            // The part starts where its first segment starts, so that is where it is until the
+            // splitting reaches a segment boundary:
+            var firstLocation = part.SourceSegments.Count > 0 ? part.SourceSegments[0].Location : default;
+            await foreach (var chunk in this.SplitTextByRulesAsync(part.Text, part.SourceSegments, strategy, 0, options, embeddingProvider, firstLocation, token, requiredPrefix, estimatedTokenCount))
+                yield return chunk;
+
+            requiredPrefix = string.Empty;
+        }
     }
 
+    /// <summary>
+    /// The parts of a text which no chunk may run across: each sheet of a spreadsheet on its own,
+    /// and any other text as a whole.
+    /// </summary>
+    /// <remarks>
+    /// Every sheet is a table of its own, with columns of its own, so a chunk which ran from one
+    /// sheet into the next would mix what two tables mean. Neither does a chunk start with the
+    /// overlap of another sheet. A sheet without a single row holds nothing but its heading and its
+    /// fences, and is left out.
+    /// </remarks>
+    /// <param name="content">The text, in the pieces its source delivered it in.</param>
+    /// <returns>The parts, in the order of the text.</returns>
+    private static IEnumerable<SegmentedText> SplitBySheets(SegmentedText content)
+    {
+        if (content.SourceSegments.All(segment => segment.Location.SheetName is null))
+        {
+            yield return content;
+            yield break;
+        }
+
+        var sheet = new List<TextSegment>();
+        string? sheetName = null;
+        foreach (var segment in content.SourceSegments)
+        {
+            if (segment.Location.SheetName is { } segmentSheetName && sheetName is not null && !string.Equals(segmentSheetName, sheetName, StringComparison.Ordinal))
+            {
+                if (TryCreateSheet(sheet) is { } completeSheet)
+                    yield return completeSheet;
+
+                sheet = [];
+            }
+
+            sheetName = segment.Location.SheetName ?? sheetName;
+            sheet.Add(segment);
+        }
+
+        if (TryCreateSheet(sheet) is { } lastSheet)
+            yield return lastSheet;
+    }
+
+    /// <summary>
+    /// The text of one sheet, joined the way the whole text was, or null when the sheet has no row.
+    /// </summary>
+    private static SegmentedText? TryCreateSheet(List<TextSegment> segments) => segments.Any(segment => segment.Location.RowNumber is not null)
+        ? new SegmentedText(string.Join("\n", segments.Select(segment => segment.Text)).Trim(), segments)
+        : null;
+
     private async IAsyncEnumerable<EmbeddingChunk> SplitTextByRulesAsync(
         string text,
         IReadOnlyList<TextSegment> sourceSegments,
@@ -130,7 +183,7 @@ internal sealed partial class TextChunker(RustService rustService, ILogger logge
         int ruleIndex,
         ChunkingOptions options,
         EmbeddingProvider embeddingProvider,
-        int? currentPageNumber,
+        SourceLocation currentLocation,
         [System.Runtime.CompilerServices.EnumeratorCancellation] CancellationToken token,
         string requiredOverlapPrefix = "",
         int? estimatedTokenCount = null)
@@ -147,14 +200,16 @@ internal sealed partial class TextChunker(RustService rustService, ILogger logge
             tokenCount = await this.GetEmbeddingTokenCountAsync(embeddingProvider, textWithOverlap, token);
             if (tokenCount <= options.MaxChunkTokenLength)
             {
-                yield return new(textWithOverlap, currentPageNumber);
+                // The whole text is one chunk, so it spans all of its segments:
+                var span = Locate(sourceSegments.Select(segment => segment.Location).ToList(), currentLocation);
+                yield return new(textWithOverlap, span.Start, span.End);
                 yield break;
             }
         }
 
         if (ruleIndex >= strategy.Rules.Count)
         {
-            await foreach (var hardChunk in this.SplitTextByHardCutAsync(text, options, embeddingProvider, currentPageNumber, token, requiredOverlapPrefix, estimatedTokenCount))
+            await foreach (var hardChunk in this.SplitTextByHardCutAsync(text, options, embeddingProvider, currentLocation, token, requiredOverlapPrefix, estimatedTokenCount))
                 yield return hardChunk;
 
             yield break;
@@ -163,7 +218,7 @@ internal sealed partial class TextChunker(RustService rustService, ILogger logge
         var rule = strategy.Rules[ruleIndex];
         if (rule.Split is null)
         {
-            await foreach (var hardChunk in this.SplitTextByHardCutAsync(text, options, embeddingProvider, currentPageNumber, token, requiredOverlapPrefix, estimatedTokenCount))
+            await foreach (var hardChunk in this.SplitTextByHardCutAsync(text, options, embeddingProvider, currentLocation, token, requiredOverlapPrefix, estimatedTokenCount))
                 yield return hardChunk;
 
             yield break;
@@ -172,7 +227,7 @@ internal sealed partial class TextChunker(RustService rustService, ILogger logge
         var units = NormalizeSplitUnits(rule.Split(text, sourceSegments.Select(segment => segment.Text).ToList()), text);
         if (units.Count <= 1)
         {
-            await foreach (var chunk in this.SplitTextByRulesAsync(text, sourceSegments, strategy, ruleIndex + 1, options, embeddingProvider, currentPageNumber, token, requiredOverlapPrefix, estimatedTokenCount))
+            await foreach (var chunk in this.SplitTextByRulesAsync(text, sourceSegments, strategy, ruleIndex + 1, options, embeddingProvider, currentLocation, token, requiredOverlapPrefix, estimatedTokenCount))
                 yield return chunk;
 
             yield break;
@@ -193,12 +248,15 @@ internal sealed partial class TextChunker(RustService rustService, ILogger logge
 
         //
         // The first rule of every strategy cuts along the segments the runtime delivered, so there
-        // a unit is a segment and carries that segment's page. Every later rule cuts inside a
-        // single segment, where all units share the page they were handed. This is what ties a
-        // chunk to a page without anybody reading the text.
+        // a unit is a segment and carries that segment's location. Every later rule cuts inside a
+        // single segment, where all units share the location they were handed. This is what ties a
+        // chunk to its pages, rows or lines without anybody reading the text. A segment without a
+        // page is on the page of the text it is part of:
         //
         var unitsAreSourceSegments = rule.UsesSourceSegmentCounts && sourceSegments.Count == units.Count;
-        int? PageOfUnit(int unitIndex) => unitsAreSourceSegments ? sourceSegments[unitIndex].PageNumber ?? currentPageNumber : currentPageNumber;
+        SourceLocation LocationOfUnit(int unitIndex) => unitsAreSourceSegments
+            ? sourceSegments[unitIndex].Location with { PageNumber = sourceSegments[unitIndex].Location.PageNumber ?? currentLocation.PageNumber }
+            : currentLocation;
 
         while (index < units.Count)
         {
@@ -212,12 +270,15 @@ internal sealed partial class TextChunker(RustService rustService, ILogger logge
                 overlapPrefix = string.Empty;
 
                 //
-                // The page of the first unit this chunk covers, not of the overlap prefix in front
-                // of it: the prefix repeats what the chunk before already said, while the page has
-                // to name where this chunk's own content begins.
+                // From the first unit this chunk covers, not from the overlap prefix in front of
+                // it: the prefix repeats what the chunk before already said, while the location has
+                // to name where this chunk's own content begins. To its last unit.
                 //
                 if (!string.IsNullOrWhiteSpace(chunk))
-                    yield return new(chunk, PageOfUnit(index));
+                {
+                    var span = Locate(Enumerable.Range(index, unitCount).Select(LocationOfUnit).ToList(), currentLocation);
+                    yield return new(chunk, span.Start, span.End);
+                }
 
                 var nextIndex = index + unitCount;
                 if (nextIndex >= units.Count)
@@ -249,8 +310,8 @@ internal sealed partial class TextChunker(RustService rustService, ILogger logge
 
             string? lastSplitUnit = null;
             var unitTokenCount = unitTokenCounts?[index];
-            var unitPageNumber = PageOfUnit(index);
-            await foreach (var splitUnit in this.SplitTextByRulesAsync(units[index], [new(units[index], unitTokenCount, unitPageNumber)], strategy, ruleIndex + 1, options, embeddingProvider, unitPageNumber, token, overlapPrefix, unitTokenCount))
+            var unitLocation = LocationOfUnit(index);
+            await foreach (var splitUnit in this.SplitTextByRulesAsync(units[index], [new(units[index], unitTokenCount, unitLocation)], strategy, ruleIndex + 1, options, embeddingProvider, unitLocation, token, overlapPrefix, unitTokenCount))
             {
                 lastSplitUnit = splitUnit.Text;
                 yield return splitUnit;
@@ -444,15 +505,48 @@ internal sealed partial class TextChunker(RustService rustService, ILogger logge
         return bestStartIndex <= chunkStartIndex ? chunkEndIndex : bestStartIndex;
     }
 
+    /// <summary>
+    /// Where a chunk starts and ends, from the locations of the units it covers, in their order.
+    /// </summary>
+    /// <remarks>
+    /// The chunk starts on the page of its first unit and ends on the last page among its units.
+    /// Its rows and lines run from the first unit which has one to the last which has one: the
+    /// heading of a sheet and the fences around a table are no row or line, so a chunk starting
+    /// with them starts at the row after them. A chunk lies within one sheet, cf. SplitBySheets.
+    /// </remarks>
+    /// <param name="locations">The locations of the units the chunk covers.</param>
+    /// <param name="current">The location of the text being cut, for what none of the units states.</param>
+    /// <returns>Where the chunk starts and where it ends.</returns>
+    private static ChunkSpan Locate(IReadOnlyList<SourceLocation> locations, SourceLocation current)
+    {
+        if (locations.Count is 0)
+            return new(current, current);
+
+        var sheetName = locations.FirstOrDefault(location => location.SheetName is not null).SheetName ?? current.SheetName;
+        var start = new SourceLocation(
+            locations[0].PageNumber ?? current.PageNumber,
+            sheetName,
+            locations.FirstOrDefault(location => location.RowNumber is not null).RowNumber ?? current.RowNumber,
+            locations.FirstOrDefault(location => location.LineNumber is not null).LineNumber ?? current.LineNumber);
+
+        var end = new SourceLocation(
+            locations.LastOrDefault(location => location.PageNumber is not null).PageNumber ?? current.PageNumber,
+            sheetName,
+            locations.LastOrDefault(location => location.RowNumber is not null).RowNumber ?? current.RowNumber,
+            locations.LastOrDefault(location => location.LineNumber is not null).LineNumber ?? current.LineNumber);
+
+        return new(start, end);
+    }
+
     /// <remarks>
     /// The hard cut is only ever reached inside a single piece of text which no rule could split
-    /// any further, so every chunk it produces sits on the page that piece was handed.
+    /// any further, so every chunk it produces sits where that piece was handed.
     /// </remarks>
     private async IAsyncEnumerable<EmbeddingChunk> SplitTextByHardCutAsync(
         string text,
         ChunkingOptions options,
         EmbeddingProvider embeddingProvider,
-        int? currentPageNumber,
+        SourceLocation currentLocation,
         [System.Runtime.CompilerServices.EnumeratorCancellation] CancellationToken token,
         string requiredOverlapPrefix = "",
         int? estimatedTokenCount = null)
@@ -530,9 +624,10 @@ internal sealed partial class TextChunker(RustService rustService, ILogger logge
                 throw new InvalidOperationException(string.Format(TB("The chunk size configured for the embedding provider '{0}' is too small: the smallest piece the text can be cut into still has {1} tokens, while the limit is {2}."), embeddingProvider.Name, smallestCandidateTokenCount, options.MaxChunkTokenLength));
             }
 
+            // A hard cut works inside a single piece of text, so the chunk stays where it is:
             var chunk = AddOverlapPrefix(text[startIndex..bestEndIndex].Trim(), overlapPrefix);
             if (!string.IsNullOrWhiteSpace(chunk))
-                yield return new(chunk, currentPageNumber);
+                yield return new(chunk, currentLocation, currentLocation);
 
             if (bestEndIndex >= text.Length)
                 yield break;

app/MindWork AI Studio/Tools/Services/Indexing/TextSegment.cs

@@ -5,5 +5,5 @@ namespace AIStudio.Tools.Services.Indexing;
 /// </summary>
 /// <param name="Text">The text of the piece.</param>
 /// <param name="TokenCount">Its token count for the embedding provider, when the source already knows it.</param>
-/// <param name="PageNumber">The page it is on, or null when the source has no pages.</param>
-internal sealed record TextSegment(string Text, int? TokenCount, int? PageNumber);
+/// <param name="Location">Where it is: its page, its sheet and row, or its line; nothing when the source does not say.</param>
+internal sealed record TextSegment(string Text, int? TokenCount, SourceLocation Location);

app/MindWork AI Studio/Tools/Services/LocalIndexSearchService.cs

@@ -103,11 +103,13 @@ public sealed class LocalIndexSearchService(SettingsManager settingsManager, Rus
             }
 
             var collectionName = DataSourceEmbeddingNames.GetCollectionName(dataSource.Id);
+            var indexStore = await databaseClientProvider.GetIndexStoreAsync(token);
+            var hiddenChunks = await this.GetHiddenChunksAsync(dataSource, indexStore, token);
             var results = filter is null
-                ? await vectorStore.SearchEmbeddingAsync(collectionName, vector, maxMatches, token)
-                : await vectorStore.SearchEmbeddingAsync(collectionName, vector, maxMatches, filter, token);
+                ? await vectorStore.SearchEmbeddingAsync(collectionName, vector, maxMatches, hiddenChunks, token)
+                : await vectorStore.SearchEmbeddingAsync(collectionName, vector, maxMatches, filter, hiddenChunks, token);
 
-            return this.LimitSearchResults(dataSource, "vector", results, maxMatches);
+            return await this.CompleteLocationsAsync(dataSource, indexStore, this.LimitSearchResults(dataSource, "vector", results, maxMatches), token);
         }
         catch (OperationCanceledException) when (token.IsCancellationRequested)
         {
@@ -281,6 +283,67 @@ public sealed class LocalIndexSearchService(SettingsManager settingsManager, Rus
         return true;
     }
 
+    /// <summary>
+    /// The chunks of a data source which its vector search must not find, cf. IndexStoreClient.GetHiddenChunksAsync.
+    /// </summary>
+    /// <remarks>
+    /// Without the index store, nothing is hidden. Its keyword search fails then as well, which the
+    /// retrieval reports, and a hidden chunk is still text of its document, only perhaps not the
+    /// version the document is searched by.
+    /// </remarks>
+    /// <param name="dataSource">The data source to search.</param>
+    /// <param name="indexStore">The index store.</param>
+    /// <param name="token">The cancellation token.</param>
+    /// <returns>The hidden chunks, document by document.</returns>
+    private async Task<IReadOnlyList<HiddenChunks>> GetHiddenChunksAsync(IIndexedDataSource dataSource, IndexStoreClient indexStore, CancellationToken token)
+    {
+        if (indexStore.IsAvailable)
+            return await indexStore.GetHiddenChunksAsync(dataSource.Id, token);
+
+        logger.LogWarning(
+            "Searching the vectors of data source '{DataSourceName}' ({DataSourceId}) without hiding incomplete generations, because local RAG index '{DatabaseName}' is unavailable.",
+            dataSource.Name,
+            dataSource.Id,
+            indexStore.Name);
+
+        return [];
+    }
+
+    /// <summary>
+    /// Completes the hits of the vector search with where their chunks are, as the index store keeps it.
+    /// </summary>
+    /// <remarks>
+    /// The vector store keeps only the pages of a chunk; its sheet and rows, its lines and the
+    /// attachment of a mail it is from are kept in the index store alone. One query for all hits.
+    /// Without the index store, the hits keep their pages, which is what they said before: a hit
+    /// which cannot say where it is still belongs into the answer.
+    /// </remarks>
+    /// <param name="dataSource">The data source searched.</param>
+    /// <param name="indexStore">The index store.</param>
+    /// <param name="results">The hits.</param>
+    /// <param name="token">The cancellation token.</param>
+    /// <returns>The hits, in their order.</returns>
+    private async Task<IReadOnlyList<VectorSearchResult>> CompleteLocationsAsync(IIndexedDataSource dataSource, IndexStoreClient indexStore, IReadOnlyList<VectorSearchResult> results, CancellationToken token)
+    {
+        if (results.Count is 0 || !indexStore.IsAvailable)
+            return results;
+
+        try
+        {
+            var locations = await indexStore.GetChunkLocationsAsync(dataSource.Id, results.Select(result => result.ChunkId).ToList(), token);
+            return results.Select(result => locations.TryGetValue(result.ChunkId, out var location) ? result with { StoredLocation = location } : result).ToList();
+        }
+        catch (OperationCanceledException) when (token.IsCancellationRequested)
+        {
+            throw;
+        }
+        catch (Exception exception)
+        {
+            logger.LogWarning(exception, "Could not read where the chunks found by the vector search of data source '{DataSourceName}' ({DataSourceId}) are. They name their pages only.", dataSource.Name, dataSource.Id);
+            return results;
+        }
+    }
+
     private IReadOnlyList<T> LimitSearchResults<T>(IIndexedDataSource dataSource, string searchName, IReadOnlyList<T> results, int maxMatches)
     {
         if (results.Count <= maxMatches)

app/MindWork AI Studio/Tools/Services/MailPassage.cs

@@ -1,3 +1,5 @@
+using AIStudio.Tools.Databases;
+
 namespace AIStudio.Tools.Services;
 
 /// <summary>
@@ -5,4 +7,5 @@ namespace AIStudio.Tools.Services;
 /// </summary>
 /// <param name="MailId">The id of the mail.</param>
 /// <param name="Text">The text of the chunk.</param>
-internal sealed record MailPassage(string MailId, string Text);
+/// <param name="Location">Where the chunk is in its mail, e.g., on which page of which attachment.</param>
+internal sealed record MailPassage(string MailId, string Text, ChunkLocation Location);

app/MindWork AI Studio/Tools/Services/MailSearchHit.cs

@@ -1,3 +1,4 @@
+using AIStudio.Tools.Databases;
 using AIStudio.Tools.Databases.IndexStore;
 
 namespace AIStudio.Tools.Services;
@@ -7,4 +8,5 @@ namespace AIStudio.Tools.Services;
 /// </summary>
 /// <param name="Summary">What a list of mails shows about the mail.</param>
 /// <param name="Passage">The passage of the mail which matched the query best, or null when the mails were listed without a query.</param>
-public sealed record MailSearchHit(MailSummary Summary, string? Passage);
+/// <param name="PassageLocation">Where that passage is in the mail, e.g., on which page of which attachment, or null without a passage.</param>
+public sealed record MailSearchHit(MailSummary Summary, string? Passage, ChunkLocation? PassageLocation = null);

app/MindWork AI Studio/Tools/Services/MailboxRetrievalService.cs

@@ -248,20 +248,20 @@ public sealed class MailboxRetrievalService(SettingsManager settingsManager, Dat
         var vectorChunks = vectorTask.Result;
         var keywordChunks = keywordTask.Result;
         var (passages, hasMore) = RetrievalPaging.Merge(
-            BestPassagePerMail(vectorChunks.Select(chunk => new MailPassage(chunk.ParentFileId, chunk.Text))),
-            BestPassagePerMail(keywordChunks.Select(chunk => new MailPassage(chunk.ParentFileId, chunk.ChunkText))),
+            BestPassagePerMail(vectorChunks.Select(chunk => new MailPassage(chunk.ParentFileId, chunk.Text, chunk.Location))),
+            BestPassagePerMail(keywordChunks.Select(chunk => new MailPassage(chunk.ParentFileId, chunk.ChunkText, chunk.Location))),
             passage => passage.MailId,
             page,
             pageSize);
 
         hasMore = hasMore || MayHoldMoreMails(page, pageSize, chunkWindow, vectorChunks.Count, keywordChunks.Count);
 
-        var passageTexts = passages
+        var bestPassages = passages
             .DistinctBy(passage => passage.MailId, StringComparer.Ordinal)
-            .ToDictionary(passage => passage.MailId, passage => passage.Text, StringComparer.Ordinal);
+            .ToDictionary(passage => passage.MailId, StringComparer.Ordinal);
 
         var summaries = await indexStore.GetMailSummariesAsync(mailbox.Id, passages.Select(passage => passage.MailId).ToList(), token);
-        return new(summaries.Select(summary => new MailSearchHit(summary, passageTexts[summary.MailId])).ToList(), hasMore, []);
+        return new(summaries.Select(summary => new MailSearchHit(summary, bestPassages[summary.MailId].Text, bestPassages[summary.MailId].Location)).ToList(), hasMore, []);
     }
 
     /// <summary>

app/MindWork AI Studio/Tools/Services/PassageRange.cs

@@ -0,0 +1,14 @@
+namespace AIStudio.Tools.Services;
+
+/// <summary>
+/// The rows or lines a passage spans, as far as it names them, cf. DataSourceLocalRetrievalService.LocatePassage.
+/// </summary>
+/// <param name="Start">The first row or line, or null when the passage names none.</param>
+/// <param name="End">The last row or line, or null when the passage does not go on beyond its first one.</param>
+internal readonly record struct PassageRange(int? Start, int? End)
+{
+    /// <summary>
+    /// The passage names no rows or lines.
+    /// </summary>
+    public static readonly PassageRange NONE = new(null, null);
+}

app/MindWork AI Studio/Tools/Services/ProvenanceCleanupService.cs

@@ -0,0 +1,87 @@
+using AIStudio.Chat;
+using AIStudio.Settings;
+using AIStudio.Tools.DataBackup;
+using AIStudio.Tools.Databases;
+using AIStudio.Tools.Databases.ProvenanceStore;
+
+namespace AIStudio.Tools.Services;
+
+/// <summary>
+/// One-shot startup service that removes from the provenance store what no stored chat refers to, see ProvenanceCleanup.
+/// </summary>
+public sealed class ProvenanceCleanupService(DatabaseClientProvider databaseClientProvider, DataRestoreService dataRestoreService, ILogger<ProvenanceCleanupService> logger) : BackgroundService
+{
+    /// <summary>
+    /// When this run of the app started. Entries stored since belong to it and stay.
+    /// </summary>
+    private readonly DateTimeOffset startedAt = DateTimeOffset.UtcNow;
+
+    /// <summary>Waits for the data directory, performs one cleanup pass, and then exits.</summary>
+    /// <param name="stoppingToken">Host shutdown token.</param>
+    protected override async Task ExecuteAsync(CancellationToken stoppingToken)
+    {
+        while (string.IsNullOrWhiteSpace(SettingsManager.DataDirectory) && !stoppingToken.IsCancellationRequested)
+            await Task.Delay(TimeSpan.FromSeconds(1), stoppingToken);
+
+        if (stoppingToken.IsCancellationRequested)
+            return;
+
+        //
+        // A restore which the runtime could not finish leaves chats and store of two different states
+        // in the data folder, while the chats it replaced wait elsewhere to be moved back. Nothing
+        // tells then which chat refers to what:
+        //
+        if (SettingsManager.DataDirectory is { } dataDirectory && DataRestoreFollowUp.IsRestoreUnfinished(dataDirectory))
+        {
+            logger.LogWarning("A restore is not finished yet, so the provenance startup cleanup waits for a later start.");
+            return;
+        }
+
+        try
+        {
+            var store = await databaseClientProvider.GetProvenanceStoreAsync(stoppingToken);
+            if (store is NoProvenanceStoreClient)
+            {
+                logger.LogInformation("The provenance store is not available, so its startup cleanup has nothing to do.");
+                return;
+            }
+
+            //
+            // A restore at this start may have brought back the chats of one moment and kept the store
+            // of another, e.g., from a backup without the store. Then the time of the last cleanup
+            // tells nothing about the chats, and every chat is read:
+            //
+            await dataRestoreService.StartupStateLoaded.WaitAsync(stoppingToken);
+            var lastCleanup = dataRestoreService.Report is null ? await store.GetLastCleanupAsync(stoppingToken) : null;
+
+            //
+            // SQLite works synchronously behind its async methods, and every changed chat with entries
+            // is read once, so the whole pass runs on a thread of its own:
+            //
+            var result = await Task.Run(() => ProvenanceCleanup.CleanUpAsync(
+                store,
+                WorkspaceBehaviour.ReadAllChatLocations(),
+                (workspaceId, chatId) => WorkspaceBehaviour.LoadChatAsync(new(workspaceId, chatId)),
+                WorkspaceBehaviour.GetChatWrittenAt,
+                this.startedAt,
+                lastCleanup,
+                stoppingToken), stoppingToken);
+
+            logger.LogInformation("The provenance startup cleanup removed {OrphanedCount} entries of chats which no longer exist and {UnreferencedCount} entries their chats no longer refer to. It skipped {SkippedCount} unchanged chats.", result.Orphaned, result.Unreferenced, result.Skipped);
+
+            // A chat which could not be read is read again at the next start, as long as the time of this cleanup is not noted:
+            if (result.Unreadable is 0)
+                await store.SetLastCleanupAsync(this.startedAt, stoppingToken);
+            else
+                logger.LogWarning("The provenance startup cleanup could not read {UnreadableCount} chats, which keep all their entries. The next start reads them again.", result.Unreadable);
+        }
+        catch (OperationCanceledException)
+        {
+            // The app is shutting down; the next start cleans up.
+        }
+        catch (Exception exception)
+        {
+            logger.LogWarning(exception, "The provenance startup cleanup failed. The next start tries again.");
+        }
+    }
+}

app/MindWork AI Studio/Tools/Services/RustService.Retrieval.cs

@@ -293,7 +293,7 @@ public sealed partial class RustService
         {
             if (segment.TokenCount is { } tokenCount)
             {
-                yield return new(segment.Content, tokenCount, segment.PageNumber);
+                yield return new(segment.Content, tokenCount, segment.Location);
                 continue;
             }
 
@@ -306,7 +306,7 @@ public sealed partial class RustService
             var countedSegment = await this.GetTokenCount(embeddingProvider, segment.Content, token);
             if (countedSegment is { Success: true } counted)
             {
-                yield return new(segment.Content, counted.TokenCount, segment.PageNumber);
+                yield return new(segment.Content, counted.TokenCount, segment.Location);
                 continue;
             }
 
@@ -318,7 +318,7 @@ public sealed partial class RustService
         }
     }
 
-    private async IAsyncEnumerable<(string Content, int? TokenCount, int? PageNumber)> StreamArbitraryFileDataCore(
+    private async IAsyncEnumerable<(string Content, int? TokenCount, SourceLocation Location)> StreamArbitraryFileDataCore(
         string path,
         string tokenizerPath,
         PromptInjectionSource? reportAs,
@@ -427,13 +427,13 @@ public sealed partial class RustService
                 }
 
                 //
-                // The count and the page come from the processed event, not from the event which
-                // was just read: a reader may hold content back across several events, and the
-                // count and page of the content it releases describe that content, not the event
-                // that released it.
+                // The count and the location come from the processed event, not from the event
+                // which was just read: a reader may hold content back across several events, and
+                // the count and location of the content it releases describe that content, not the
+                // event that released it.
                 //
                 if (!string.IsNullOrWhiteSpace(processedEvent.Content))
-                    yield return (processedEvent.Content, processedEvent.TokenCount, processedEvent.PageNumber);
+                    yield return (processedEvent.Content, processedEvent.TokenCount, processedEvent.Location);
             }
         }
         finally
@@ -442,7 +442,7 @@ public sealed partial class RustService
         }
 
         if (finalContentChunk is { } pendingContent && !string.IsNullOrWhiteSpace(pendingContent.Content))
-            yield return (pendingContent.Content, pendingContent.TokenCount, pendingContent.PageNumber);
+            yield return (pendingContent.Content, pendingContent.TokenCount, SourceLocation.OnPage(pendingContent.PageNumber));
 
         if (promptInjectionRedactedCount is 0)
             yield break;

app/MindWork AI Studio/Tools/Services/TemporaryChatService.cs

@@ -23,17 +23,17 @@ public sealed class TemporaryChatService(ILogger<TemporaryChatService> logger, S
             return;
         }
 
-        this.StartMaintenance();
+        await this.StartMaintenanceAsync();
         while (!stoppingToken.IsCancellationRequested)
         {
             await Task.Delay(CHECK_INTERVAL, stoppingToken);
-            this.StartMaintenance();
+            await this.StartMaintenanceAsync();
         }
     }
 
     #endregion
 
-    private void StartMaintenance()
+    internal async Task StartMaintenanceAsync()
     {
         logger.LogInformation("Starting maintenance of temporary chat storage.");
         var temporaryDirectories = Path.Join(SettingsManager.DataDirectory, "tempChats");
@@ -65,13 +65,42 @@ public sealed class TemporaryChatService(ILogger<TemporaryChatService> logger, S
             if(deleteChat)
             {
                 logger.LogInformation($"Deleting temporary chat storage directory '{tempChatDirPath}' due to maintenance policy.");
-                Directory.Delete(tempChatDirPath, true);
-                WorkspaceBehaviour.InvalidateWorkspaceTreeCache();
+                await this.DeleteTemporaryChatAsync(tempChatDirPath);
             }
         }
 
         logger.LogInformation("Finished maintenance of temporary chat storage.");
     }
+
+    /// <summary>
+    /// Deletes one temporary chat the way the user deletes a chat, so that what it received goes along.
+    /// </summary>
+    /// <remarks>
+    /// A chat which cannot go now, e.g., since another operation holds it or a file of it is open,
+    /// stays until the next maintenance. Its failure must not end this service, nor the app with it.
+    /// </remarks>
+    /// <param name="tempChatDirPath">The directory of the chat.</param>
+    private async Task DeleteTemporaryChatAsync(string tempChatDirPath)
+    {
+        try
+        {
+            if (Guid.TryParse(Path.GetFileName(tempChatDirPath), out var chatId))
+            {
+                if (!await WorkspaceBehaviour.DeleteChatWithoutAskingAsync(Guid.Empty, chatId))
+                    logger.LogWarning("The temporary chat '{ChatId}' is busy, so the next maintenance deletes it.", chatId);
+
+                return;
+            }
+
+            // Not a chat AI Studio made, so nothing else knows about it:
+            Directory.Delete(tempChatDirPath, true);
+            WorkspaceBehaviour.InvalidateWorkspaceTreeCache();
+        }
+        catch (Exception exception)
+        {
+            logger.LogWarning(exception, "Could not delete the temporary chat storage directory '{Directory}'. The next maintenance tries again.", tempChatDirPath);
+        }
+    }
     
     public static void Initialize()
     {